Brake lights on constantly

[GLOOPY]

I have a problem with the brake lights on my 420 staying on, lighting up as soon as the ignition is on without any pedal pressure. The car has standard rear lights and a 'Just Add Lightness' high level brake light. Just passed an MoT and all the lights have worked satisfactorily for over 1500 miles.

I thought the problem would likely lie with the brake light switch but oddly this is working but in the reverse sense i.e. when pressed the lights extinguish. I changed the switch for a new metal one from Car Builders, as recommended on this forum for other brake problems, with the same result. Swapping the connections over on the switch does not make a difference. There is clearance between the switch and the plate attached to the pedal, it does not make a difference if the switch is loose from the pedal box.

The brake light circuit is very simple and I cannot think of a reason why the switches would work in the reverse sense. 

Car electrics are not a strong point of mine, am I missing something obvious? 

David

[Jonathan Kay]

OK. Rugby over. Interesting problem.

1 Do you have a multimeter and would you like a wiring diagram?

2 Everything was working fine at one time, and there hasn't been any work anywhere that might have caused this? 

3 Ignition ON. Gearbox not in reverse.

 • Disconnect the wires from both terminals of the switch. Are the brake lights ON or OFF? Are any other lights ON, even dimly?

• Touch the bare ends of the wires together. Are the brake lights ON or OFF? Are any other lights ON, even dimly?

• Separate the bare ends. Are the lights ON or OFF? Are any other lights ON, even dimly?

Jonathan

[SM25T]

It is working fine as you described. It must be adjusted so when pedal at rest the plunger is just pushed, extinguishing the lights. Then when pedal is pressed, plunger is released and lights illuminate.

[Golf Juliet Tango]

As #3, I think this is a mechanical issue not an electrical one.

 

[Jonathan Kay]

If the tests in #2 come out with typical results (which I expect) then we'll know,,,

Jonathan

[SM25T]

It works fine. Just set the switch in the right place on the bracket. No further forensics needed.

[John Vine]

#1 ...when pressed the lights extinguish.

As explained above, this is how it's meant to work. 

JV

[anthonym]

ditto - catches me out every time for a few seconds.

I always expect push (the switch) to illuminate and it's the opposite, I always wonder why. Not that it doesn't work very nicely just as it is and easy to set up. anthony

[GLOOPY]

Well, a lesson in not jumping to conclusions. Refitted the switch as advised and it works fine. My thanks to all.

Jonathan, I have a wiring diagram but thank you for the offer.

David

[SM25T]

Good news