As fitted to 405′s, 406′s and possibly some late 403′s
The overdrive interrupter switch on the gearbox was originally listed as 31077E but was superceded by Lucas to 30451. The significant difference in various differently numbered variations of this switch was apparently the electrical terminals. Some had post terminals, some had wide spade terminals, some had standard spades and some had the terminals bent over to the side. The 30451 has standard spade terminals that stick straight up.
NOTE: 31077E is also the reverse lamp switch on a 406 and presumably 30451 is therefore a straight substitute. This is often listed on EBay and is a “relatively” common switch.