are brake lights & headlights linked?

morgan73 · Unread post by **morgan73** » 03 Apr 2004, 19:53

Help! My brake bulb needed changing. I did that and now every time I brake my headlights come on as well. What have I done? How the hell did that happen?!
Xantia 97 1.9TD

JohnD · Unread post by **JohnD** » 03 Apr 2004, 21:31

I would start by removing the bulb that's just been replaced, and try again, making sure it's the right way round and sitting correctly across the two contact points.

AndersDK · Unread post by **AndersDK** » 03 Apr 2004, 21:54

In line with John -
Have you fitted a single filament bulb, in a 2-filament bulb socket ?

morgan73 · Unread post by **morgan73** » 04 Apr 2004, 00:05

I bought a twin pack of bulbs about 6 months ago when I needed one for the other side. I used that and had no problems so I assume the bulb's the right one.

chemexhants · Unread post by **chemexhants** » 04 Apr 2004, 20:46

Anders is quite correct. The bulb you have replaced should be a twin filament unit for tail and brake light. By replacing it with a single filament bulb, when the brake pedal is pressed the current can only activate the tail light circuit which, by creating a short circuit, also activates the headlamp on the side that you have replaced the bulb.
Change the bulb to a twin filament one and the problem will be resolved, and you will not be flashing at too many other drivers!!!

morgan73 · Unread post by **morgan73** » 04 Apr 2004, 21:58

Thanks everyone. I've changed the bulb (it was single filament) and everything works fine now. I still can't figure out why it worked ok in the other side though [?]

JohnD · Unread post by **JohnD** » 04 Apr 2004, 23:19

But a single filament bulb wouldn't work correctly. The correct bulb is a 21/5. 21 for the brake light and 5 for rear light.