My 90 F-150 4x4 has the guages, and when it's cold the Alt guage drops to 8V and the lights get dim. I have shut everything down, and it has no effect. Ireplaced the Alternator and no dice. It only does this when it's cold outside. It will majically fix itself after 5 minutes or so of driving. The battery doesn't seem to be affected, because it starts every time. A couple times I hit the dash and it worked, so could there be a gremlin under there, or is it coincidence? Someone once mentioned a pigtail I should have replaced, but fumbling with the wires does not good. Ideas?

 

Yes, it's Gremlins.
When cold, my oil guage doesn't move for a few minutes, then shoots up to correct reading.
Dealer scratched his head when I asked about it. Decided not to gamble and have them mess around with something they didn't seem to know anything about.
Good luck, hope you find a solution.