Front side lights come on when braking

[focusdriver]

On my mk1 focus the front side lights come on each time I brake. This has happened ever since I replaced the passenger brake light. Apart from looking silly to oncoming drivers everytime I brake and the risk of giving out wrong and unintended signals, would this cause my car to fail an mot?

[focusdriver]

Oh and is there a fix for this!

[maniac0796]

A. Did you put the bulb in correctly. If it was a twin filament, is it the right way round? They have a right and a wrong way round.

B. Are the connections clean inside the bulb holder

C. Is the earth in the wiring plug for that side clean.

It will be one of these answers most likely.

[Ozzie Osmond]

You've fitted the wrong brake light bulb.

Check carefully (by looking at the contacts on the base of the right side brake light bulb) and start again.

[focusdriver]

Thanks, I will double check the bulb and clean the connections.

[MissChief]

What focus driver said. Happened with my mums old Micra. Fitted the wrong brake light bulb and every time she touched the brake pedal lights on the dash would light up!

[Rex Ironstone]

I had a MB (Chrysler) van at my last job and I swear one of the headlights came on when braking. And if you had your foot on the brake with the lights on you could turn the key and remove it and the engine would keep running until you took your foot off the brake. Weird.

[paintman]

Could also be a faulty bulb. Had this on the Range Rover.

[redvictor]

Ozzie Osmond said:

You've fitted the wrong brake light bulb.

Check carefully (by looking at the contacts on the base of the right side brake light bulb) and start again.

What he said, and it could be the wrong way round depending on what year and model.
It's amazing how many people get such a simple task wrong...

[jagracer]

You've put a twin pole bulb in a single pole socket or vice versa.

[SamT1993]

maniac0796 said:

A. Did you put the bulb in correctly. If it was a twin filament, is it the right way round? They have a right and a wrong way round.

This had one at work like this and yes it will fail MOT

[Mr2Mike]

jagracer said:

You've put a twin pole bulb in a single pole socket or vice versa.

Only one of these combination would cause a problem (single filament bulb in twin filament socket).

[jagracer]

Mr2Mike said:

jagracer said:

You've put a twin pole bulb in a single pole socket or vice versa.

Only one of these combination would cause a problem (single filament bulb in twin filament socket).

OK, I bow to your superior knowledge.

[AJB]

Mr2Mike said:

single filament bulb in twin filament socket.

or

paintman said:

Could also be a faulty bulb. Had this on the Range Rover.

or

the earth wire to the rear light cluster has become loose or damaged when you changed the brake light bulb.

[focusdriver]

Mr2Mike said:

jagracer said:

You've put a twin pole bulb in a single pole socket or vice versa.

Only one of these combination would cause a problem (single filament bulb in twin filament socket).

Turns out that I put a single pole bulb in a twin pole socket. Replaced with twin filament bulb and all OK. The brake lights were also permanently on when I switched on the headlights which I hadn't noticed before. I can't believe having a wrong bulb in would cause other lights to come on. Thanks everyone.

[Rollcage]

Feeds back through the base of the bulb into the sidelight circuit. Had exactly this on a Transit I was asked to look at the other day.

[Pontoneer]

You're braking far too hard and the G force is throwing all the electrons meant for the brake lights to the front of the car !

Ye cannae change the laws of physics cap'n .