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.

2 Litre Ignition Timing

Ignition Timing

There has been a lot of talk concerning how to set timing with an unknown engine. I think a basic description of timing might help sort out a lot of this. First, you should know that there are two types of timing in an engine: cam timing and ignition timing. (Three types, if you count injector pulse, but injection timing on gasoline-powered buses is tied to ignition timing and is not separately adjustable so I will ignore it, as should you.) Cam timing is what determines when the valves open and close with respect to the position of the pistons in their bores. It is set when the engine is built- by placing the camshaft and crankshaft in the correct relationship.

It cannot be adjusted on a stock engine. It doesn’t change: if it was right once it will be right for the life of the engine, barring disaster. And by disaster I mean the park-it-where-stops-rolling kind of disaster. (This is a very rare occurrence in VW air-cooled engines. Not so rare in the Rabbit/Golf ones, which drive the cam with a rubber belt which strips if you don’t change it on schedule.) In summary, cam timing is not connected with or affected by the turning of the distributor. What distributors time is spark, or ignition. Why?

At idle, your engine is turning relatively slowly, let’s say 650 rpms. The throttle is closed, so very little fuel and air are being drawn in to the cylinders. This small amount of combustible mixture burns very quickly, so for maximum efficiency, the spark needs to start when the piston is very near top dead center (TDC). If the spark comes too early (i.e. too advanced), the pressure from the ignited mixture will hit the piston while it is still coming up the cylinder and be wasted trying to shove the piston down before it reaches the end of it’s travel. If you try to start an engine whose ignition timing is too advanced, the starter will try to turn the crank one way, and the combustion process will try to turn it the other way, and it will seem as if the starter hasn’t enough oomph to start it. Contrariwise, if the timing is set too late (too retarded), the pressure from the ignited mixture (and the power derived therefrom) will dissipate as the flame front chases the piston down the cylinder bore in the rapidly diminishing pressure of the combustion chamber.

In other words, the piston is already on it’s way towards the bottom of it’s stroke, reducing the effectiveness of combustion. The is very fuel inefficient, since a larger throttle opening at idle (set by the idle speed screw) is needed allow extra fuel in to keep the engine idling. In practical terms, the position of the distributor which yields the highest idle speed is within a very few degrees of where it should be set. (If you retard the timing about 5 degrees from this point, you will be awfully close to spot-on.) Of course, this assumes your carburetor (or Fuel injection)is working well and that the idle mixture is correct.

When driving on the highway, your engine’s timing requirement is different. At higher engine speeds, larger throttle openings and greater loads than idle, you need ignition advance. There are two reasons for this. First, you are burning more fuel so complete combustion takes longer. Second, the combustion time, as a percentage of the time the piston is at or near top dead center is much longer because of the piston speed. What this means is that you have to ignite the charge earlier, while the piston is still coming up, in order to get the full benefit of the pressure against the piston at the right time. Too early or too late timing will have a similar effect at speed as at idle, but greatly magnified and with far more destructive potential. Too retarded timing will give low power, lousy emissions and excessive bore wear. Timing too advanced will cause pinging (a rattling noise usually heard on acceleration), overheating cylinder heads and other problems too scary to contemplate.

I will now pretend that vacuum advance (not fitted to 2 litre Distributors) doesn’t exist, otherwise it will only confuse things. Distributors have little weights inside that swing away from the shaft as it turns faster. As they move out, they rotate the upper part of the shaft which passes through the plate that the points are bolted to so that the rubbing block which opens the points meets the lobes which hit it (and thus open the points) a little earlier.

At what engine speed this advance begins, at what rate it advances and at what engine speed it stops advancing is determined by the shape and mass of the advance weights and the strength of their return springs; at what degree of advance it stops is determined by a limiter on the plate to which the weights are bolted . None of this is meant to be adjusted: the manufacturer sets it up for each engine family it builds, based on compression, cam profile, octane requirements and availability, among other things. Timing the ignition, then, is a matter of getting the timing correct at one end (idle or full advance) and letting the rest of the range look after itself.

If you have a stock distributor and know either the timing at idle or the maximum advance at a given engine speed and you have a good timing light, you will have no trouble setting timing. If not, here are some ways to get in the ball park. I already mentioned that the highest idle speed is very slightly advanced from correct. If you set it there and hear no pinging on acceleration and get good power (ha-ha), you are good. If it pings, retard it little by little until the pinging goes away. If it seems weak, advance the timing a little at a time until you hear pinging or find the engine hard to start, then retard it again.

400-406 Dynamo’s (Generators)



Warning – When working on your dynamo or indeed at any time whilst the engine is running, keep your hands well away from the fan blades!

YouTube Videos
Dynamos are often referred to as a generators. If the dynamo has been off the car for a considerable time, or your car has been standing for a considerable time, your Dynamo may require polarizing. Here are two YouTube videos on the subject.

YouTube Video 1

YouTube Video 2

Is My Generator Charging?

If you have a voltmeter, here are some easy tests to make – Measure the voltage across the battery, it should be about 12.6 volts with the engine off. As the engine speeds up, the voltage should increase to somewhere around 14 volts. If it does, the generator is working and charging the battery. If the voltmeter does not go up with the engine running, first check to see that the generator brushes are not worn excessively. If you can, apply a little pressure to the brushes while the engine is running and see if the gen light goes out or the voltmeter reading increases. If it does, the brushes may be worn to the point that they don’t exert enough pressure on the commutator.

Generator Testing

If the brushes check OK, do this test: Disconnect the generator from the regulator (probably easiest to simply take the wires off the generator). Connect a jumper from DF on the generator to the generator frame. Now run the engine and measure the voltage from ground to D+ on the generator. NOTE: Some generators have different types of terminals; verify which is DF and which is D+. As you increase the engine speed, the voltage should jump up to +35 volts or so (@3000 RPM). If it passes this test, the generator is good. (Don’t run this test longer than necessary as it will overheat the generator.)

If it fails that test, the generator may need to be polarized. Leave the jumper wire connected from DF to ground. Remove the fan belt. Connect a wire from the battery + terminal to D+ on the generator. The generator shaft should start to spin. Don’t run this way for more than a few seconds to avoid overheating. The generator will now be properly polarized. If the generator did not spin during this motoring test, the generator is likely defective. Put the belt back on and re-test for generator voltage with DF grounded. If the output voltage is still low, the generator is defective.

About Polarizing

Why do generators need to be “polarized”. Auto generators need some magnetism to get started. This “residual” magnetism remains in the Field pole pieces even after the engine has stopped. The next time the generator starts up, the residual magnetism creates a small voltage in the Armature windings. Not enough to charge the battery, but enough to allow the Field windings to draw current. As the Field current increases, the pole pieces create even more magnetism. That makes even more voltage in the Armature, and the cycle continues until the generator is capable of producing maximum output.
What happens though to a generator which has been stored a long time or is freshly built? The residual magnetism may have decreased to the point where it can no longer get the generator started producing voltage. In the case of a new generator or one which has been mis-treated, the residual may even be of the wrong direction (North and South poles reversed). Polarization is a simple process used to restore the Field pole residual magnetism and ensure the magnetic direction is correct.

Do regulators need to be polarized?
No, regulators are not polarity-sensitive. But my regulator came with instructions to polarize it… These instructions actually polarize the generator, not the regulator. The regulator mfr simply wants to ensure that your generator will work properly so you don’t blame the regulator.

Generator Diagnostics & Troubleshooting

Generators must spin clockwise to make voltage. They won’t make voltage if they are spun counter-clockwise. Generators always make some voltage when they are spinning. The red Generator light in the dash is an important part of the charging system. The system will not charge if the light is bad or not hooked up. The ignition powers the light, the Generator grounds it when not charging. This makes the light stay on. Here’s how the connections on the voltage regulator go and what they mean: (NOTE: this may depend on your type of regulator)

B = Power out of the regulator to the car and battery
F = Generator Field Winding
WL = Warning Light
D = Generator (actually D is for Dynamo) output
E = Ground to the body (actually E is for Earth)

So, make sure the wide spade connectors are on the “B” terminals. Make sure that there is continuity in the F and D wires. In other words, unplug the D wire from the back of the Generator and unplug it from the voltage regulator. Now take an Ohm meter and touch the leads to each end of the wire, you should get a small amount of resistance which shows the wire isn’t broken. Now do the same test on the F wire.

If those are both okay, hook them back up to the Generator. Now leave them off the regulator. Bridge them with a short piece of wire and using a voltage meter, put the pos. lead of the meter into one of the ends that you’ve bridged. Touch the black test lead on the meter to the battery ground. With the engine running at about 1,000rpm+ you should get 18 volts. (This is called “full fielding the generator”)

If you get 18 volts, the Generator is fine and you have a bad regulator if you get less than 18 volts, you have a bad Generator….for whatever reason. They are extremely easy to repair. New brushes and springs are dirt cheap and take abot 15 minutes to replace. Polish the commutator with fine sand paper while your’re in there and finally, I cannot stress enough the need for clean, tight, and large, engine and body grounds. If you want to check them touch the leads of your Ohm meter to the engine block and to a screw going into the body in the engine compartment somewhere. You should get nearly zero Ohms. Any other reading shows bad grounds. Do the same test between the battery ground POST and a screw going into the body on the inner fender. Do the same test between the “E” terminal on the Voltage Regulator and the body in the engine compartment.

401-406 Brake switch

Model 54C ? Lucas 31281B 5 64

This switch is also used as a reversing lamp switch in many applications.

31281B is listed as fitted to the following :

  • AC 16hp Saloon 1948-51
  • Allard ‘J’ 1951-52 ; ‘K’, ‘L’, ‘M’ and ‘P’ 1949-51
  • Alvis 14hp 1949-50
  • Armstrong Siddeley Hurricane, Lancaster 1946-53, Whitley 1950-53
  • Aston Martin 2litre 1947-50, DB2 1951-54
  • Austin 8hp, 10hp, 12hp 1946-47, 16hp 1946-48
  • Austin A40 Devon 1948, A90 Atlantic 1949-52, A125 Sheerline 1948-54,
  • A135 Princess 1948-57
  • Bristol 2litre 1947-48, 400 1949-50, 401 1949-53, 403 1954, X404 (Arnolt Body) 1954
  • BSA FWD Three Wheeler and Scout models 1931-40
  • Citroen 15hp 1946-53, 23hp 1946-55
  • Daimler 36hp 1946-53, 2.1/2litre 1946-53, Consort 1950-53, 3litre 1953, Conquest and Century 1954-58
  • Dellow 1952-54
  • Healey 16hp Saloon and Roadster 1948-49
  • Hillman Minx 1946-54, Minx Series III 1955-57, Husky Series I 1955-57
  • HRG 9hp and 12hp 1946-52
  • Humber Hawk 1946-54, Imperial 1946-54, Snipe 1946, Super Snipe 1946-52
  • Jaguar 1.1/2litre 1946-48
  • Jensen 3.3/4litre 1946-47
  • Jowett Javelin 1948-54, Jupiter 1951-54, 10cwt Bradford Van 1946-54
  • Lagonda 2.1/2litre 1949-52, 3litre 1954-58
  • Lanchester 14hp 1952-53, 10hp LD10 1946-51
  • Lea Francis 14hp 1946-54, 18hp 1951-54, 1.1/2litre and 2.1/2litre Sports 1950-54
  • Morgan Plus Four 1946-50
  • Morris 8hp 1946-48
  • Paramount Roadster and Coupe 1946-52
  • Riley 1.1/2 1946-55, 2.1/2litre 1947-52
  • Rover 10hp, 12hp, 14hp and 16hp 1946-47, ‘60’ 1948-56, ‘75’ 1948-56, ‘90’ 1954-56
  • Landrover 1948-59
  • Singer 9hp Roadster 1946-51, 1200cc 4AC and 4AD 1952-55
  • Standard 8hp, 12hp and 14hp 1946-48
  • Sunbeam Alpine 1955-56, MkIII 1955-56
  • Sunbeam-Talbot 10hp, 2litre 1946-47, ‘80’ 1948-50, ‘90’ 1948-52
    Trojan 1946-60
  • Wolseley 8hp, 10hp, 12hp,14hp and 18hp 1946-48, 25hp 1948