Brake light switch

[Robbiee]

Does anyone know if the etype brake light switch fits (ie same thread) a 1963 MGB??

[Heuer]

The usual recommendation is to use an OEM VW Beetle switch for its reliability. An even better course of action is to fit a mechanical switch activated by the brake pedal as it is instant on and very reliable if you use a BMW or Volvo switch. You can leave the original switch in place as a sort of parallel backup. Details in the Upgrades Forum.

[christopher storey]

Robbie : yes, MGB is perfectly ok. All these switches seem to use the same BSP thread, and I presume that Heuer's preferred VW switch also uses it since this suggestion has been made many times before

[Robbiee]

Thanks chaps
My MGB needs a new one and the latest ones from SNG are supposed to be better(according to Butlins) so I thought that might be a good option

[Heuer]

Actually the VW switch has a slightly different thread (tapered IIRC) but it fits, does not leak and is reliable. Having said that SNGB have put a lot of work into re-engineering the hydraulic switch so that would be my first choice for your MGB.

[Tom W]

What thread is the MGB switch? Despite being used across various British cars, and looking superficially similar, there are several thread sizes BSP, NPTF, UNF etc. If you get the wrong one, you risk damaging the thread in the union and/or having the joint leak. I’m not sure about the MGB, but for E-types not all the unions are readily available should you damage one.

The VW switch is almost certainly metric, and so shouldn’t be used. It appears to fit because the pitch close enough for the thread to start, but as it’s different, eventually it binds and that’s why it feels like it’s tight. As they’re incompatible parts, you can’t guarantee it’s properly sealing the way a tapered thread should.

[Heuer]

Andrew has some experience of using the Beetle switch:
viewtopic.php?p=144161#p144161

VW Part numbers are: #113-945-515/H or #113-945-515/G. Threads are M10 x1 which is very close to the 3/8 BSP thread.

Regardless I would only recommend the mechanical switch upgrade nowadays. The VW trick was only if you were caught short of lights whilst touring Europe.

[Tom W]

I believe the Jaguar switch is 1/8” NPT tapered. This is 27 TPI, or a pitch of 0.941mm. The metric thread pitch 1mm, or 25.4 TPI. Not that close really. For example, with a 1/4” thread engagement, there’s a mismatch of just under 1/2 of a tooth.

[mgcjag]

Hi All.....I looked into these thread sizes some time ago..........So been in contact with SNG....very helpefull......the thread on the new uprated brake switch is the same as the old switch and it is 1/8 NPT(tapered).......the original 4 way unions are 3/8 unf 24 with one port for the switch being 1/8 NPT..... The new style 4 way have all ports as 3/8 unf 24 so the new uprated switch will not fit.......

There is an adaptor available part no BQ247 from Brakequip and others that have a female 1/8NPT to male 3/8-24unf that you could possibly use to fit the new switch into the new 4 way..but i havent tried it..... Steve