Headlight switch diagnosis

[JHZR2]

Car is 1993 300SD (W140). Have had a variety of electrical issues, hoping my lighting issue is just the switch. Essentially, if I set the switch to parking lights, all taillights illuminate. If I put the switch to full on for headlights, some of the taillights stay on, but not all.

I also lost my headlight indicator lamp in the cluster. Probing the lamp, the ground is good, but I don’t see 12v at the socket.

While a used or an aftermarket switch is really cheap, I’d like to understand if it’s really the cause. Any thoughts on if what I’m seeing is due to the switch? I would think that lights that are on in both positions would have one path for electricity to flow, but maybe not…

Is this a situation to throw the part at it?

Thanks!

[jsb357]

W123 had issues I thought were switch related and were not

Check grounding points at both front corners and at trunk (boot)

get a wiring diagram and check all wiring and do not assume connectors are properly
assembled if it's a used car.

If it was working for you at some point it might just be a grounding issue.

Get a DMM digital multi-meter roll your sleeves up.

if you take anything apart use di-electic grease upon reassembly