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MG Midget and Sprite Technical - Brake Lights Blowing Fuses

All of a sudden one of the fuses has started to blow whilst driving, I have found it blows as soon as the brake pedal is pressed and after removing both brake light bulbs the problem persists so I am assuming either the brake light switch or the wiring has a short somewhere.

One of the few things original on my 1500 is the brake light switch but it looks like it's finally failed. As many drivers have had to replace theirs when it fails does it usually blow the fuse and with all the issues reported with the Chinese replacements has anyone got any decent replacements?

Thanks
Tim



Tim Lynam

It's unusual for the switch to blow the fuse, unless it's developed an internal fault where it is shorting to earth.

If you have a multimeter, it would be a good idea to disconnect the brake light switch completely and check for continuity between each wire and earth, both with the brakes off and also applied. If you do have continuity in any of those conditions, your switch is faulty.

If not, check for continuity between the green/purple wire that enters the loom and earth with the brake light bulbs removed. If there is continuity, you have a wiring fault.
Dave O'Neill 2

Thanks Dave, I do have a multimeter but my electrical know how is pretty awful and don’t really follow how to check for continuity if the brake switch is disconnected then there’ll be no power going through the wires to the rear of car, it’s probably obvious to 98% on here but not me!
Tim Lynam

Sorry, I probably didn’t make it clear. The first test is for the switch. You are just checking to make sure it isn’t shorting to earth.
Similarly, the second test is also checking that the wiring isn’t shorting to earth. You don’t need any power for the test.
Dave O'Neill 2

Cheers Dave, will investigate further.
Tim Lynam

The continuity test of the brake switch when removed proved the switch to be working well, but one of the short wires connected to the switch was found to have a brake in the insulation and was shorting against the body of the car.
After insulating the cable and re fitting the switch all now works well.

Thanks again Dave for the info and a valuable lesson learnt.
Tim Lynam

Glad you’ve found the problem.

Are you going on Thursday?
Dave O'Neill 2

Yes will be at Matlock on Thursday, hope to see you there?
Tim Lynam

This thread was discussed between 07/08/2023 and 08/08/2023

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