This is a true story about my 2003 Ranger. Happened a few years ago.
One day I noticed the dome light was on.
Of course, the first thing I did was to go around and slam the doors shut.
Then I started to play with the switch in each one of the doors.
I couldn't see anything wrong with the switches, so I lubricated them with WD40 to make sure there wasn't any dirt in them.
I tried to figure out what was wrong with the electrical system, so I took off the fuse cover and checked all the fuses and the connections. I was able to locate the fuse that would turn off the light, and thought about leaving the cover off so I could pull the fuse when the truck sat. Since the fuse operated other things, I didn't think I could do that.
I was really worried that I'd be at work and have the battery run down with the light left on. So, figuring I had no choice, I finally called the dealer.
The dealer said he'd had problems like this before. I needed to come in for a systems check and there would be at least $150 in parts and labor to fix the switch system.
I hated it, but I couldn't think anything I could do futher so I started to try to find some extra money.
The next day my wife hopped into the truck with me to go somewhere and I told her about the dome light.
Since she has an 05 Ford car, she said, "Isn't the dome light switch at the top of the dash dimmer?"
...uh...yes it was...