If you run out of other possibilitiies and are about to give up, look under the drivers side carpet. There is a taped bundle (Renix) of wires that kind of just runs under the carpet and the splices get green and short out. One of the signs, is a dim but constant on dome light.
If you have electric seats and are under there anyway, look at the seat wires that run under the carpet and over the hump to the passengers side, they also sometimes corrode and short.
I`ve also seen the wires to the back of a door switch get twisted during installation and cause problems. Have you recently replaced any switches?
I had one Renix, that if the rear dome button switch was switched on, all the dome lights would stay on. Don't know how many times I shut the last door and the light stayed on, I'd then try the headlight switch, then ended up walking around the back to turn the rear dome switch off (the kids would switch it on, the first time was really interesting). I've seen all sorts of differnt rear dome light setups, yours may not be the same.
The dome light switch inside the rear hatch in the Renixs, often turns to a big clump of rust. The wire rotted off both of mine and was hanging loose.