cars

Anybody got any reasonably good ideas/sources on how to troubleshoot an intermittent issue where the rear running lights (and license plate light) don't light up while the headlights are turned on during times of day when it is cool/cold and damp? Which, coincidently is when it is dark outside making this issue very inconvienient.

Breaklights work, blinkers work, hazards work. Bulbs are okay.

Checked all the fuses and replaced the headlight control switch. Things worked yesterday afternoon when it was sunny and hot but not today in the early AM while its cool and damp.

I've never "tested the grounding" and haven't had the time to skim through every "how to" video to weed out all the ones that just say to check fuses/bulbs and then take it to a mechanic.

One of the rear light covers is cracked. Would there be a chance that condensation in there would be enough to short out the running light circuit but not all the other light circuits?