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1979 Mark V Electrical Issues

Hello Bill,
I have a Collectors Series Mark V that until lately was trouble free, however, one recent night the headlights stopped working. I was about 5 miles from home when the headlights and dash lights went black and the switch was non responsive. I did some research and thought that the headlight switch needed replaced so I purchased one from Lincoln Land and installed it but nothing changed. After that the fuses and circuit breakers were replaced but that didn’t make a difference.
The car starts and runs fine but there are no headlights, parking lights, or interior lights. The brake lights do work as do the hazard flashers. When we lost the lights several other things quit working as well: headlight doors, power seats, passenger compartment lighting, seat back releases, power locks (windows work).
Any idea what I should try next?
Thank you in advance.
Hello Rob –
Your question should not be ” any idea what I should TRY next?” but it should be ” how can I DIAGNOSE this electrical problem?” The only way to diagnose a problem such as this is to trace the power path of the lighting circuit etc. with the use of the correct wiring diagram at your side and a 12v test light. Guessing and replacing parts until the fault goes away is costly and time consuming. Your problem could turn out to be as simple as a bad connection at a junction or a failed fuse link near the starter relay under the hood. Fuse links are special lengths of fuse wire that is carefully spliced into the power distribution area usually near the battery. You will need to read the diagram correctly and know the location of the items to be examined and tested. The above method is the best and only way find the culprit. Let us know what you find.

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