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MG MGA - Brake Switch Thread


What is the size and thread of the brake switch in the engine compartment, the one with the two wires going to it?


Garreth
Garreth

Garreth - The original size was 1/8 BSP (straight), however it seems that some of the replacements are a tapered thread. They will work but require a lot of teflon pipe tape to seal really well.

If you are replacing the switch, be aware that replacement switches are light duty junk that will burn out with a flashlight bulb on them. Put a relay and a arc suppression circuit between the new switch and the brake lights to keep the switch working. Instruction on making up a relay and arc suppression circuit are available at: http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
Good luck - Dave
David DuBois

Now you made me look, and I just removed the pressure switch from my car to be sure.

The pressure switch thread is 1/8 BSP TAPERED, not straight. The BSP threads are usually tapered for pressure tight seal.

There is also a straight form for the BSP thread standard for longscrew threads threads, but I have no idea what it's used for. When using the straight thread a copper sealing washer and a shoulder on the fittings is required for sealing, or otherwise use a backnut against a socket to seal the threads.

If you are buying a brake light pressure switch through an aftermarket supplier, be careful to get the right one. 1/8 BSP is 28 threads per inch, 1/8 NPT is 27 threads per inch, and they are NOT interchangable.

Barney
B Gaylord

Hello Garreth,

If you are in North Kent let me know and you can come round and have a look.

Regards

David
David tTownshend

I agree with David the original brake pipe thread was I think straight, although I have seen many now that have been modified to tapered. The MGB was tapered and so was the midget, therefore all the ones bought now and supplied are tapered. You can buy new brake light switches from any motor parts stores or factors. They all tend to be 1/8thBSPT
Bob (robert)

This thread was discussed between 06/04/2005 and 11/04/2005

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