Wiring diagram – Late V8’s 412 to Beaufort

Thank you to Jeff Marsh for providing the following wiring diagrams:

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Classic Car Keys

This company can supply any of the Bristol key patterns, either as a duplicate or to a code.  The code can be found on the barrel of the lock.  This does entail removing the barrel from the lock.

Wilco Direct

Unit D1/D2, Pinetrees Road, Pinetrees Business Park, Norwich, Norfolk, NR7 9BB

Website

Classic car key page at time of writing

Email address

Lucas Electrical fault diagnostics

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Chrysler 360 Rotomaster ignition

The Chrysler 360 Rotomaster turbocharged version fitted to about 30 Beaufighters and 25 Brigands apparently has a major flaw in engine control systems as originally configured and supplied by Bristol and Rotomaster. The flaw is with ignition timing which needs to be massively retarded under boost conditions, and the set up originally supplied by Bristol is very hit and miss. If the ignition is not retarded quickly enough by the distributor set up then you get massive detonation.

Any turbo charged car maintained by Bristols or where the owner has taken advice from them will have been fitted with a MSD Ignition system (part number MSD 6BTM) which is controlled by a MSD control knob (part number 6BTM 6462). The control knob allows the user to dial in the extent of retard under boost conditions from NIL to 3 degrees per pound of boost pressure. Once set up correctly the knob is best hidden, at least from a retard like me. You will of course appreciate why straightaway! The exact set up depends on fuel quality used and the set up of the turbo wastegate.

Below are copies of the instruction manuals. Please click the appropriate heading to download a copy.

Click here to download (TYPE, 1.8MB)

V8 ignition switch

RELAYS AND OTHER RELATED ISSUES

INTRODUCTION

 Recently, it was reported on various Bristol Forums, that owners of at least one model, the 411, were experiencing Ignition Switch failures. Initially, these parts were replaced, only to have a similar issue a short time later. Understandably, owners were less than pleased after the replacement failed again, and this article attempts to illustrate the reasons why, and to recommend a remedy, that is well proven.

 

Having been employed at a leading company in the Motor Industry in Coventry for over thirty years, reliability testing was a major part of my engineering activities. This involved the logging of prototype vehicle test data to prove out the various electrical components. The information thus gathered then gave an indication of the vehicle lifetime expectancy of each item, and this could be used for warranty investigations later on, if required.

Major electrical loads were monitored during the tests, including air conditioning, cooling fans, external lighting, heated rear screen, heated front screen, electric windows, seat heaters, and in-car entertainment ( radio/ amplifiers, TV etc.). Data from component suppliers was also analysed, to ensure that, for example, the ignition switch, was being operated under electrical load conditions appropriate to the supply company’s recommendations. Also, back emf (the spark that appears across the contacts) at switch-off, did not exceed the limit outlined in DIN57-879. This Europe-wide specification relates to radio frequency interference by induced transients from inductors, ie, motors and solenoids, and requires sufficient suppression to be fitted to eliminate the effect.

The table below, illustrates some of the issues involved, with measurements taken before and after suppression components had been added, clearly demonstrating an improvement and compliance with the DIN regulation, (36V max @ 1mS duration).

 TABLE  A

Component

Transient  at switch-off  before suppression

Transient  at switch-off  with suppression

Seat motor

– 232v @ 1 mS duration

– 31v @ 0.5 mS duration

Cooling fan

-183v @  0.5 mS duration

– 32v @ 0.4 mS duration

Air Con fan (interior)

– 247v @ 0.4 mS duration

– 34v @ 0.35mS duration

mS = mille-second

Over time, the energy generated across relay contacts at switch-off from unsuppressed components, will burn away the contact faces, and lead to switch/relay failure. Adding the suppression improved the reliability of the circuit components, and thus reduced failures to a minimum. Good for customer satisfaction.

A similar approach was taken with external lighting, where values obtained for the switch-on current of filament lamps were also measured. These included sidelights, head and fog lamps. The following table gives some of the results that could be applied to the wiring systems of Bristol cars:

TABLE  B

Bulb

In-rush current at switch     ON – AMPS

Illuminated/rated current – AMPS

H4 – Dip beam 55 watts

45 peak @ 10mS

4.58 @12v nominal

H4 – Main beam 60 watts

50 peak @  10mS

5.00 @ 12v nominal

Indicator 21 watts

17.5 peak @  10mS

1.75 @ 12v nominal

Sidelight 5 watts

  4.1 peak @ 10mS

0.41 @ 12v nominal

Also, the value of current that could be reliably passed by the ignition key switch was determined to be approximately 20 amperes. To switch more than this limit, several load relays were introduced to power up the various vehicle systems controlled by “Ignition ON “. These included headlamp flash, headlamps, fog lamps, heated rear/front screens, air conditioning, seat motors, In-Car entertainment systems, and fuel injection/engine management.  The circuitry included fusing for each relay controlled load, and reduced the amount of current directly switched by the ignition key. This reduced the probability of electrical failure of the ignition switch by a considerable margin. Also, the impact of Vehicle Construction and Use Regulations, and Federal (USA) NHTSA legislation, led to circuit evaluation for compliance. For example, all cigar lighters at that time, were required to be switched by the ignition key, and driving/ fog lamps if fitted, were to be switched in pairs, and not individually. These legislative requirements were subsequently incorporated into the circuitry.

BRISTOL SPECIFIC ISSUES

Ignition switch

This is sourced from a Range Rover application amongst others for the 411 model, but the following set of conditions leading to failure, would apply to most other vehicles produced by Bristol with similar wiring/circuitry. Excessive loading leading to early contact failure, especially with the cigar lighter sockets being used to power up various items such as games and DVD players for the rear seat passengers, combined with heated rear window current, plus the usual driving aids such as demisters, windscreen wipers, and cooling fans, will cause the ignition switch contacts to fail after a short time. This is exactly what happened previously.

The following re-routing of the circuits is applicable to most of the later cars from 408 onwards, as the wiring is terminated in the right hand wing locker, and the circuit colours can easily be identified and modified. Of course, when designing circuitry for a new vehicle, one relay would supply two or three additional loads, however, when modifying existing wiring, individual load relays are easier to include without a major strip out of the wiring looms.

See Appendix 1 for the wire colour designations, these follow the old Lucas wiring colours, but for some applications, owners should consult the vehicle handbook/workshop manual for specifics.

The following Key-In Ignition ON loads supplied directly from the ignition switch should be removed, and powered up via an additional relay

1)     Heated rear window;

2)     Electric windows;

3)     Air conditioning(where fitted);

4)     Cooling fans

5)     Cigar lighters (where applicable)

 

This then leaves the ignition circuits, wiper motor plus the radio, (without external/ additional amplifiers) at about 12 – 14 amps, that is well within the load capability of the key switch.  .

 

HEADLAMP FLASHER

 

This is a function of the indicator switch stalk. However, the contact rating is about 10 amps on my car (a 408 MkII), and looking at the current in-rush values for the main beam filaments in Table B, it can be seen that flashing four headlights results in a combined in-rush current of 190 amps for 10mS duration, after which the steady current is 19 amps, almost twice the rating of the switch. Also, the voltage at the lamps is reduced, and hence the light output, because the cross sectional area of the wiring to the flasher switch is too small. This is another circuit that requires a relay to switch the filament load.

COOLING FAN

The supply to this circuit should be removed from the ignition switch as previously discussed, and the following additional modification ought to be carried out. The cooling fan circuit utilises a thermal switch manufactured by Otter, situated in the radiator header tank. This switch controls the fan relay, and will fail if the relay coil is not suppressed. The back emf (spark), generated at switch off on an unsuppressed relay, is typically as high as 92 volts for 2mS duration. This appears across the thermal switch contacts that open relatively slowly when compared to similar relay contacts. The slow opening speed draws an arc across the air gap as the contacts move apart, and erodes the mating faces. Eventually, with carbon build up, the contacts when made will be of a high resistance, and the relay will fail to operate because of it. Therefore, a 0.1 microfarad capacitor should be wired in parallel with the relay windings to eliminate the issue. These suppressors are readily available from accessory suppliers

 

CONCLUSION

The only modifications that I have carried out to my own vehicle, a 408 MkII, are the suppressor modification on the cooling fan relay, a headlamp flash relay with a fuse in the power feed, fog lamps paired up with their own relay, and changed the starter relay for a plug-in type, as the original had burnt contacts. Additional fuses have been fitted in the headlamp circuit, the front fog lamp pair, and the rear fog lamp pair. As my vehicle is without a heated rear screen, the cooling fans remain wired through the key-switch as is, the load current is about 10 amperes. All of the applications discussed previously, can use relays sourced from Jaguar parts suppliers, See Appendix 2.( NB The cigar lighters on my vehicle are powered directly via a fuse from the battery, and therefore are not controlled by Ign-ON.)

When attempting to modify the circuitry, it is recommended that the cheaper alloy type of lucar spade terminations are not used, as electrolytic corrosion will ensue in damp conditions, owing to two dissimilar metals being brought together in the cable crimp, ie copper and aluminium. Always use either brass or tinned brass for these crimped terminations. Again, these are available from companies that advertise in classic car publications and the Internet.

Regarding the 411 ignition switch failures. These occur because the original circuit design did not take into account the maximum current that could be reliably switched by the contacts. Having the air conditioning on, with the wipers and demisters running, plus the heated rear screen and other accessories being powered from the cigar lighter socket(s), would probably produce a back emf at switch-off, that would easily erode the contact faces of the switch element in a relatively short time. Changing the switch again is only a short term solution, and the only effective method to eliminate premature failure, is to apply the circuit changes discussed in this article.

 

APPENDIX 1 – Wire colours

Many British designed vehicles use colour coded cables to assist in identifying the various circuits in use. This is an extract from BS-AU7a 1983 Colour Code for Vehicle Wiring, from the British Standards Institution, 2 Park St., London W1A 2BS.

(Note that these colour codes may not apply directly to older cars. For example, the wipers on cars up to 1980 (at least) are not on a separate fuse circuit, so they are not orange, but green. Check the schematic for your car to be certain.)

 

TRACER PURPOSE
Black All earth connections
Black Purple Temperature switch to warning light
Black Green Relay to radiator fan motor
Black White Brake fluid level warning light to switch and handbrake switch, or radio to speakers
Black Orange Radiator fan motor to thermal switch

 

TRACER PURPOSE
Blue Lighting switch (head) to dip switch
Blue Brown Headlamp relay to headlamp fuse
Blue Red Dip switch to headlamp dip beam fuse
Fuse to right-hand dip headlamp
Blue Light green Headlamp wiper motor to headlamp wash pump motor
Blue White a) Dip switch to headlamp main beam fuse
b)Headlamp flasher to main beam fuse
c)Dip switch main beam warning light
d)Dip switch to long-range driving light switch
Blue Yellow Long-range driving light switch to lamp
Blue Black Fuse to right-hand main headlamp
Blue Pink Fuse to left-hand dip headlamp
Blue Slate Headlamp main beam fuse to left-hand headlamp or inboard headlamps when independently fused
Blue Orange Fuse to right-hand dip headlamp

 

TRACER PURPOSE
Brown Main battery lead
Brow Blue Control box (compensated voltage control only) to ignition switch and lighting switch (feed)
Brown Red Compression ignition starting aid to switch
Main battery feed to double pole ignition switch
Brown Purple Alternator regulator feed
Brown Green Dynamo ‘F’ to control box ‘F’
MAIN TRACER PURPOSE
Brown White Ammeter to control box
Ammeter to main alternator terminal
Brown Yellow Alternator to ‘no charge’ warning light
Brown Black Alternator battery sensing lead
Brown Slate Starter relay contact to starter solenoid

 

MAIN TRACER PURPOSE
Green Accessories fused via ignition switch
Green Brown Switch to reverse lamp
Green Red Direction indicator switch to left-hand flasher lamps
Green Purple Stop lamp switch to stop lamps, or stop lamp switch to lamp failure unit
Green Light green Hazard flasher unit to hazard pilot lamp or lamp failure unit to stop lamp bulbs
Green White Direction indicator switch to right hand flasher lamps
Green Yellow Heater motor to switch single speed (or to ‘slow’ on tow- or three-speed motor)
Green Black Fuel gauge to fuel tank unit or changeover switch or voltage stabilizer to tank units
Green Pink Fuse to flasher unit
Green Slate a)Heater motor to switch (‘fast’ on two- or three-speed motor)
b)Coolant level unit to warning light
Green Orange Low fuel level switch to warning light

 

Light green Instrument voltage stabilizer to instruments
Light green Brown Flasher switch to flasher unit
Light green Blue a)Flasher switch to left-hand flasher warning light
b)Coolant level sensor to control unit
c)Test switch to coolant level control unit
Light green Purple Flasher unit to flasher warning light
Light green Green Start inhibitor relay to change speed switch; or switch to heater blower motor second speed on three-speed unit
Light green Yellow Flasher switch to right-hand warning light
Light green Black Front screen jet switch to screen jet motor

 

TRACER PURPOSE
Orange Wiper circuits fused via ignition switch
Orange Black Switch to front screen wiper motor parking circuit
Orange White Timer or intermittent unit to motor parking circuit
Pink white Ballast terminal to ignition distributor

 

Purple Accessories fed direct from battery via fuse
Purple Brown Horn fuse to horn relay when horn is fused separately
Purple Blue Fuse to heated rear window relay or switch and warning light
Purple Red Switches to map light, under bonnet light, glove box light and boot lamp when fed direct from battery fuse
Purple Green Fuse to hazard flasher
Purple Light green Fuse to relay for screen demist
Purple White Interior lights to switch (subsidiary circuit door safety lights to switch)
Purple Yellow Horn to horn relay
Purple Black Horn to horn relay to horn push
Purple Pink Rear heated window to switch or relay
Red Main feed to all circuits mastered by side lamp switch
Red Brown Rear fog guard switch to lamps
Red Blue Front fog lamp fuse to fog lamp switch
Red Purple Switches to map light, under bonnet light, glove box light and boot lamp when side lamp circuit fed
Red White a)Side lamp fuse to right-hand side and rear lamps
b)Side lamp fuse to panel light rheostat
c)Fuse to panel light switch or rheostat
Red Yellow Fog lamp switch to fog lamp or front fog fuse to fog lamps
Red Black Left-hand, side lamp fuse to side and tail lamps and number plate illumination
Red Pink Side lamp fuse to lighting relay
Red Orange Fuse box to rear fog guard switch
Slate Window lift main lead
White Ignition switch or starter solenoid to ballast resistor
White Brown Oil pressure switch to warning light or gauge, or starter relay to oil pressure switch
White Blue Choke switch to choke solenoid (un-fused) and/or choke to switch to warning light, or electronic ignition distributor to drive resistor
White Red Starter switch to starter solenoid or inhibitor switch or starter relay or ignition (start position) to bulb failure unit
White Light green Start switch to starter interlock or oil pressure switch to fuel pump or start inhibitor switch to starter relay or solenoid
White Yellow Ballast resistor to coil or starter solenoid to coil
White Pink Ignition switch to radio fuse
White Slate Current tachometer to ignition coil
White Orange Hazard warning lead to switch
Yellow a)Overdrive
b)Door locks
c)Gear selector switch to start

Relay-Picture1

Ignition System Trouble Shooting

Ignition System Trouble Shooting

Written for American MG Pages but perhaps very relevant

When your car will not start, it is frustrating. When it suddenly stops as you are driving along, the emotions range from frustration to terror (such as when it happens in rush hour.) There are two basic causes of this type of problem-lack of spark and lack of gasoline. In this article, I would like to focus on the ignition system, how to determine if it is an ignition system problem and how to troubleshoot to find out where the problem lies.

If the car dies as you are driving along, immediately look at the tachometer. If it has dropped to zero, you have a low tension ignition system fault. If it is falling, but still showing the engine speed as it falls, you have either a fuel system or a high tension ignition fault. This two second procedure can give you a good clue as to where to begin your troubleshooting.

If you are trying to start your car and it will not start, you may have either a fuel system or an ignition system problem. The easiest way to check is to disconnect the lead going from the coil to the distributor cap at the distributor cap end. Then, using a pair of insulated pliers (or a couple of sticks), hold the end near the engine block and have an assistant crank the engine over. You should get a good spark at the coil lead that will jump a gap of ¼” to ½”. If it does not, you probably have a low tension (LT) circuit problem.

To check out the LT circuit, you need a good volt-ohm meter, or VOM. You can use a test light, if necessary, but this is less desirable. An inexpensive VOM can be purchased from Radio Shack, Harbor Freight and most parts stores. Keep it in the original box and put it in the trunk with your tool kit, stored in a plastic bag to prevent moisture or dust from getting at it. The first thing to do is to determine whether you have power going to the coil from the ignition switch. The power going into the coil will go to the terminal marked SW (switch) on earlier coils and + on later coils. The chrome bumper cars will normally have one wire going to this terminal while the rubber bumper cars will have two. The first step is to simply turn on the ignition switch and measure the power input to the coil. You should have 12 V at all times. If you do not have power into the coil, you have a fault between the brown wire going to the ignition switch and the coil. This could be either the ignition switch or the wires. Use the ohm meter function to test the wires by connecting one probe to each end. On a good wire, you will read zero resistance and a bad wire will read infinite resistance.

Another method is to use the volt meter function and find out where the volts stop. Remove the steering wheel cowl and check the brown wire for current. If it does not show current, you have bad power input to the ignition switch. If you have good power input, check the various terminals of the ignition switch for power through the switch. You need a wiring diagram, preferably one that has been duplicated and expanded, for this procedure. At this point, it is simply tracing wires until you find where the voltage stops showing on the meter, then replace the wire between the last good point and the one found bad. (Note. Power to the coil, on RB cars when the car is cranking, comes from the starter. If you do not have 12V input with the car cranking, check the starter to coil wire. The car cannot be started under these conditions without jumpering the coil to a good 12V source that has constant power.

If the car starts when the key is in the start position, but dies when the key is returned to the run position, you have a white wire circuit problem and that is the area to concentrate on. The white wire circuit provides a 6V input to the coil with the ignition switch in the run position. When it goes bad, you may loose both fuel pump and coil depending on where the break is.) If, however, you find good voltage input to the coil, you proceed to the next step, checking the coil.

The common check for a bad coil is to “replace with a known good unit” in all of the better service manuals. Not very practical when stuck on the side of the road or when you do not have a “know good coil” handy. A second method is, with the ignition off, use the ohm meter to check the resistance across the coil terminals. Connect one probe to each of the terminals and read the resistance. On a 12V coil, you should read between 3.1 and 3.5 ohms resistance. On a 6V coil, you should read between 1.43 and 1.58 ohms resistance. (The Lucas 12V Sports Coil shows slightly higher resistance than the standard 12V coil, about 5 ohms on the one I tested new.) If you read zero resistance, you have a short in the coil and it is not functioning. If you read infinite resistance, there is a break in the windings and the coil is not functioning. Replace with a known good unit. If the coil tests good, continue checking out the system.

The next test is to use the volt meter to read the voltage coming from the coil with the ignition switch on. This should be between 6 and 9 volts, depending on model of coil. If it more than this, the coil is shorted internally. If it is less than this, there is too much internal resistance. Once again, replace with a known good unit. If the voltage is within limits, use the ohm meter to check the wire (power off now) between the distributor and the coil terminal. This terminal is marked CB (contract breaker) or – depending on coil vintage. You should show zero resistance. If you show infinite resistance, you have a bad wire. If you show more than a few ohms resistance, you have a broken wire or one going bad. Replace as necessary. When, or if, you have a good wire providing current from the coil to the distributor, you can begin your distributor checks.

If you have an electronic points replacement unit (the so called “electronic ignition”) there is not much that the average hobbyist, or even professional mechanic, can check. The practice here is, again, “replace with a known good unit”. This is why people who have added these units to a points type distributor should always carry a spare set of points and condenser to install if there are problems. If, however, you have a points type distributor, the tests can continue.

Turn the ignition switch to the start position, applying power to the system. Check the voltage on the wire coming to the distributor from the coil at the end of the wire, then again at the points. If the connection is loose or corroded, you will see a voltage drop between the coil and the points. If you have good voltage from the coil wire but low voltage at the points, it is the wire that goes from the terminal on the distributor to the points. I have seen these go bad, but only rarely. Next, with the point closed, check the voltage on both sides of the point’s contacts. A drop of more than one volt indicates bad points. While you are examining this area, make sure the base plate ground wire is in good condition. This wire runs from the base plate to one side of the distributor and is connected to the distributor by one of the screws which hold the base plate in place. If it is bad, the grounding of the system is less than optimal and may be the cause of your problem.

The other, main ground, for the system is the distributor clamp on the engine. The distributor must be tight (but not too tight) in the clamp and the clamp must be firmly tightened to the engine block for the system to function properly. After these checks have been completed, you should have discovered any LT circuit problems and have corrected them. The only part of the system you have not checked is the condenser. A bad condenser should not prevent the car from starting and running, it only makes it run poorly. It is rare to find a condenser tester today and, once again, the “replace with a known good unit” applies. With the LT circuit tested and functioning, it is time to move on to the high tension circuit.

The HT circuit consists of the coil, the distributor cap, rotor, coil and plug wires and the spark plugs. The first test in checking the HT circuit is to remove the wire going to the distributor cap from the coil at the cap end. Then, use your insulated handling devise to see if you get spark when an assistant cranks the engine over (as mentioned previously). If, with a known good LT circuit, you do not get a good, strong spark, either the coil or coil lead is bad. Replace the lead and try again. If still no spark, replace the coil. If however, you have a good, strong spark with the original lead (or get one when you replace the original lead), check for spark at the spark plug wire. The best way to do this is to take one of your old spark plug caps into the hardware store and get a long, threaded bolt or screw that fits it.

Use this device to verify that you have a strong spark at each plug wire. If all the wires have about the same spark, you have demonstrated that the distributor cap and rotor are in good, functional condition and the wires are good. That only leaves bad spark plugs as your source of ignition system problems. If one wire shows no spark or weak spark, it could be a distributor cap/rotor problem or a wire problem. Replace the bad wire with one of the other spark plug wires and retest. If it now shows a good spark, replace the bad wire (I prefer to replace them as a set). If that terminal shows a poor or no spark with a wire that tested good on another terminal, replace the distributor cap and rotor. Right now, we are concerned with basic function rather than best performance. A car will start and run with marginal wires.) If the wires test good, replace all the spark plugs and the car should start. If it does not, you probably have a fuel system problem.

In summary. The distributor is a two function unit. It creates, through the low tension circuit, a pulsing magnetic field within the primary windings of the coil which is a step-up transformer. It distributes this pulse of higher voltage through the high tension circuit from the coil to the spark plugs by way of the ignition wires, the rotor and the distributor cap. If the ignition system is functioning properly, after your checks, your car should start. If it does not, you need to trouble shoot the fuel system and the ignition timing.

Negative to positive Earth

How to Convert from Positive Ground to Negative Ground

NOTE: DIY may be OK and here are the steps – but you are advised to get it done by someone who KNOWS what they are doing!

1) Disconnect the wires at the generator (dynamo)
2) Swap battery connections around
3) Swap Coil leads
4) Swap Heater leads
5) Re-polarize the generator (dynamo)

Re-polarize the Generator (dynamo): To re-polarize the generator, connect a jumper wire from the positive side of the battery and touch it several times to the small terminal on the generator. You will see a small harmless spark. The generator’s magnetic field is now reversed.

Electrical Fuel Pump: Early non-diode containing electric SU fuel pumps are not polarity dependant and so they don’t need the wires switched, a positive 12 volt wire goes to the terminal on the top of the fuel pump, a gounding wire screws into the base flange of the pump body and then attaches to the wall of the trunk floor. Later replacement pumps are polarity independant (usually designated by red tape around the top points cover to indicate a positive ground pump, or black tape to indicate negative ground pump.) The diode inside the top cover of the pump will have to be removed and re-installed in the reverse direction to change these later pumps over to negative ground.

Heater Blower Motor: Swapping heater blower motor leads restores the blower to the correct spin direction.

Wiper Motor: The wiper motor is also polarity independent. No wire changes are required. However, I have read that the thrust is apparently affected and it has been suggested that the armature housing cover be rotated 180 degrees from it’s original position. This can be done by removing the 2 long screws that hold the cover in place.