One headlight doesn't work (high beams on both do) 1984 Mitsubishi Colt

Question

1984 Mitsubishi Colt with left headlight out. I tried replacing it but the unit is sealed and it's going to be a mess around if I can even find another replacement light, let alone fix the current one.

So my problem and symptoms:

• High beams work perfectly. Both holding on and switching on works a treat.
• High beam lights go through same bulb (or unit), parkers are different but work too.
• Sometimes when I turn on the lights (and dash lights/parkers), the lights for my cluster and inside car don't turn on, so I have to turn off and back on again. In this time, the headlights work fine (except of course the broken left headlight)
• Fuses all look perfect. Could switching them be any use?

Does a car like this, old and mechanical even have an extra place I can check for faults for one headlight? Could it be something in wiring rather than a burnt out bulb?

Answer 1

The fact that you get intermittent fails in unrelated systems (the cluster/interior lights) makes it sound like some kind of pesky electrical fault. I don't know the vehicle, but it likely has a large wiring harness under the steering wheel or near there for all the headlight/turn signal switches etc. Get a good wiring diagram, unplug the harness, then do continuity & voltage tests on all the major connections points.

I had a similar, infuriating issue where the headlights in my vehicle would just go out randomly. Later on they would work again but they were very unreliable. I tried replacing the master switch and a few other things. Finally just had to dig in and test every connection in that harness.

Guess what I found? One of the +12v leads to the light switch had come unplugged a bit, which caused excess heat that further degraded the harness connection, and it happened to be the one that fed the headlights. It was bad enough I had to pull the wires out and splice the connection around the harness, but the headlights worked like a charm after that.