Mysterious electrical issue

On Thursday morning, 31DEC2009 I drove to work in the dark and my dashboard instrument lights and tail-lights were working fine. The car sat idle from around noon that afternoon until early Monday morning, 04JAN2010. When I drove to work (again, in the dark) I noticed my dashboard instrument lights weren’t working, but since I could see the speedometer and gauges well enough I put fixing a blown fuse in the back of my mind and drove to work. When I got to work, however, a co-worker told me my tail-lights weren’t working.

On the way home from work, I stopped at my neighborhood car mechanic to see if I could get what I thought was a simple problem fixed. He couldn’t find any problem with any of the fuses, and I made an appointment to take the car in this weekend for both a regular oil change and to get the electrical problem fixed.

But yesterday morning, while sweeping off the light snow that had accumulated overnight, I let the car run so I could use the defrosters. Just before finishing the back of the car, I tapped lightly on the left tail light then decided to check my all my lights. After turning on the headlights, I noticed the dashboard instrument lights were working again – and so were the tail lights.

They were working when I checked them again when I got home from work and this morning, before I took the car in for the oil change, etc.

The only thing I can think that might have changed between when the lights weren’t working and when they were working is the humidity, but I haven’t a clue if that’s an issue or what else might be the problem.

Any suggestions?

Remove the bulbs (first) (remove them and shake while looking for a loose filament), check for corrosion and deteriorated wiring.

Sometimes a simple cleaning will do the trick.

The Ford products I have owned have the tail lights and the dash lights on the same circuit. I once had a heater blower fuse that would sometimes make the connection and sometimes not. I would be tempted to splurge and replace the fuse that controls the tail lights and dashlights

I’ll check the tail light bulbs for corrosion, but I don’t believe they’re connected in series with the dashboard instrument lights, so I doubt that even if corrosion were the problem with the tail lights that wouldn’t affect the dashboard lights.

As to this possibly being a fuse issue, both my mechanic and I have checked each fuse – even those not listed as being related to these lights – and nothing’s wrong with any of them.


The lights are connected in parallel, not series, so if one light goes blows out the others still have full power getting to them and stay on.

The trouble you are having is most likely due to a lack power getting to the lights from a common point. The fuse for the lights is one point to check and it appears that is ok though you didn’t state you proved power was getting to the fuse. Only that the fuse is ok. The other common point to check for a problem is the light switch itself. Using something like a test light probe to check where power is getting to is a good thing to use.

I had a similar problem with a 96 Contour. It turned out to be a break in the wiring just aft of the headlight switch.

Thanks! I’m thinking that it’s something to do with the switch. Very strange; I’ve been unable to see any patterns: low humidity, but not all the time; high humidity, but not all the time; same with low and not-so-low temps, smooth and rough roads, etc. But this morning when I turned on the headlight switch, the lights didn’t come on, so I turned it off and when I turned it back on, voila’ – so did the lights. Maddening. Tomorrow, it’ll be in the shop again. Thanks for validating my own hunch.