A Matter Electric

The recent installation of European H4s on my 1983 SC, together with the necessary relays, lead me into the not-unfamiliar territory of finding another problem crop up just as I thought I was done. The trail to the solution was one which was not hard to follow, but also one from which many of us have strayed. So I thought I would share with you the experience and diagnosis as an object lesson, one which employs two principles of automotive tinkering: 1) Keep it simple and start with the basics; and 2) If it worked before, ask yourself what have you touched recently that is remotely related to it which could now be all buggered up?

After I installed a factory socket and relay for the high beams, and a relay from Hella (found lurking in my pile of stuff left over from other projects) for the low beams, my fog lights would not work. The pull-out switch would glow, but no “click” from the relay, and no light from the fogs. Armed with my factory service manuals and a test light I went to work. First shot was at the relay for the fogs. I replaced it with another that was laying around (for some reason I had bought a box of four at Stoddard’s swap meet three years ago). Still no fogs. Then I went through the wiring diagrams for the regular lights and then the supplemental diagram for the installation of fogs on an SC.

After more than a few trips back and forth between the front of the car and the diagrams laying on my workbench I satisfied myself that all was properly wired. The only deviation from standard US wiring for fog lights was the attachment for the relay “trigger wire” from the circuit for the low beams to the circuit for the parking lights which allows the fogs to come on whenever the parks are on, not just low beams. (Please do not tell the DOT.) I had done this before the H4 installation, so it was not suspect in this analysis. Was the switch bad? I began to have ugly thoughts of taking it out of the dash and messing with the wiring in the cramped confines behind the speedo. Then reason prevailed.

Bearing in mind the above principles I went back to basics and checked the ground on one of the fogs by energizing the circuit and taking it straight to ground. Voila! That fog lit up and the other did not. So I pursued the grounding gremlin and first determined that the common ground for the fog lights was untouched and solid. But there is another ground in this circuit: the ground for the fog relay. When I installed the Hella relay for the low beams I discovered that I had mounted it where the fog light relay grounds. When I did so I did not get the ground wire back in a way that gave it a metal-to-metal contact; it was against paint and plastic. Reassembly made the ground good and the fog lights then worked. Had I just checked the power source and the condition of the grounds first I would have saved myself hours of fooling around. Once the ground was fingered as the culprit all I had to do was employ principle number 2 above and I would have been lead straight to the second relay installation.

I also took the opportunity while I was feeling competent in matters of wiring and electrons to wire up the “city lights” in the Euro H4s. Pretty neat effect. The headlights just glow now when the parking lights are energized.

© W. S. Cline/Rose Lane Garage 2000


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