Hi all, I'm new to this forum as earlier attempts to register have failed. Could really do with some help with an electrical problem I have. Currently building an Avon and cannot solve the following issue. With the ignition switched on if I press the brake pedal brake lights come on but also all the instrument lights as well. If I then switch the lights on the brake lights come on and stay on. With lights switched on the is constant 12v supply to the brake circuit.
I've got a very limited knowledge of auto electrics and am really struggling to sort this problem out, any help would be really appreciated.
Thanks

Colin

The brake lights should be controlled by either a hydraulic switch somewhere in the brake pipe routing or be momentary push switch on the brake pedal. Either way, with the ignition switched on there should be a 12v feed to the brake lights and then the earth wire routed via the switch to earth (chassis). Pushing pedal should then activate the switch and complete the brake light circuit, switching them on.

It sounds like you may be feeding the brake lights from the wrong 12V feed.

Check the earth on the rear lights. If thats failed it'll back feed brake to side lights and vise versa. Same thing can be caused by having single contact bulbs fitted when they should be double contact/double filament or by faulty bulbs.

Adrian

Sounds like a short between sidelights and brakelights - as adithorp says, check the bulbs & holders for wrongly fitted bulbs or dodgy holders.

Thanks for the replies. I don't think there is an issue with the bulbs or clusters, I've removed one completely so only have the loom spades exposed. Constant 12v supply to brake light wire when lights switched on. nothing when lights switched off. Brake lights are operated by a hydraulic switch screwed into the master cylinder, with the lights off 12v supply to one side of the switch but with lights on I'm getting 12v on both sides of the switch, I don't think this is right.

So have you checked both lights?

Adrian

All sorted now thanks, sure enough when I checked the other rear light the bulb was shorting across the tail and brake connection, realigned bulb and the problem has gone away.

Thanks for the advice

Colin