A-class headlamp problem

[marksmith]

Hi folks,

My girlfriend's W168 A-class has developed a headlamp fault. The left-hand headlamp has no main beam.

High beam works on both left and right. Sidelights work on left and right. Main beam works only on right.

The fuse (number "1") under the panel by the door is good, and the bulb is good. I can measure 12v at the top terminal of fuse 1 when I switch the main lights on. I cannot measure any voltage at the appropriate terminal on the bulb holder.

Any ideas please? Are there any troublesome connectors between these two points? Or common failure points? The wiring is basically completely inaccessible in this car so I'm dreading having an awkward problem.

Thanks!
-Mark

 

[alec2]

There is probably a relay involved somewhere.

Easy to replace

Alec

 

[area51]

There are no relays for lighting on the W168, all switching is done by the light switch/module.

Possibly a light switch fault?? Or dirty/burnt contacts in the switch?

 

[mattkh]

High beam works on both left and right. Sidelights work on left and right. Main beam works only on right.Thanks!
-Mark

Hi
Put a new bulb on.

 

[marksmith]

Thanks for the replies. As mentioned, the bulb is good - really

There are no relays for lighting on the W168, all switching is done by the light switch/module.

Possibly a light switch fault?? Or dirty/burnt contacts in the switch?

This is very useful, thanks. I just found out that the fusebox by the door is part of the light switch, not a separate thing, by the way - useful to know.

 

[mattkh]

Hi
On your A class, is the main beam on a separate bulb, i.e. not the same bulb as the high beam, ?

 

[area51]

Personally I would change the bulb first just to be certain that it is ok.

Then possibly remove and strip the headlight switch and clean the contact points.

One other possibility is a damaged wiring connector on the switch.