W124 side and rear light mystery

[crt]

I wonder if someone can help with this problem I am experiencing with my ‘95 e300d estate?

I have lost right hand side, rear and dash lights, and everything else on fuse 3.

The fuse is fine. I have 12v on a multimeter at the bottom of the fuse (ie, the feed to the circuit), but when I attach a bulb I have nothing, suggesting a fragile connection somewhere between the switch and the fuse box, which allows 12v but fails under load. The circuit works if I bridge from any live circuit, inc fuse 8 (the left hand lights).

I’ve stripped down the fuse box and the problem persists at the grey wire feeding fuse 3.

Before I strip out the headlamp switch, has anyone experienced something similar? I believe the lights route through a relay - could it be this? Also, if I can’t trace problem with feed, where would be the best place to tap in a substitute feed - back at the switch, at the relay (where?) or possibly from fuse 8 (my initial view is that the feed does not look big enough to support both circuits, but views welcome).

Thank you.

 

[crt]

I’ve now fixed this. The grey feed to fuse 3 comes, according to the wiring diagram, directly from the rotary headlamp switch. I extracted the switch, located the grey, cut it, and soldered a new 8amp wire to the switch end, threaded it through a convenient hole through the bulkhead behind the switch which comes out under the fuse box and terminated it at fuse 3. I still don’t know why the original grey failed as it goes straight in the loom at either end, but fail it had.

 

[Blobcat]

I’ve now fixed this. The grey feed to fuse 3 comes, according to the wiring diagram, directly from the rotary headlamp switch. I extracted the switch, located the grey, cut it, and soldered a new 8amp wire to the switch end, threaded it through a convenient hole through the bulkhead behind the switch which comes out under the fuse box and terminated it at fuse 3. I still don’t know why the original grey failed as it goes straight in the loom at either end, but fail it had.

MB fitted some decomposing wiring insulation for awhile in the 90’s so it might have suffered with that.

 

[DREAMER NO2]

The light control unit [relay] is in rear of fuse box

 

[crt]

Thanks. Interesting. For a 27 year old car, the electrical problems have been quite limited - this one with the lights, a melted heater fuse housing (switched circuit to an unused neighbouring housing), replace fuses with copper, intermittent radio feed (aftermarket end probably), and a shorting rear wiper (currently disconnected and awaiting replacement or further diagnosis and repair). Oh, and infra-red central locking control giving up, alongside door key not working, so just replaced with cheap key-less entry system, necessitating getting under rear seat and splicing various wires at the vacuum control unit.