Now a month ago I started having problems with it staying on more constantly and I just got use to having the relay out and not having a dome light. For the last two weeks if I let the truck sit more then a day the battery dies on me. Today I hooked up an amp meter and started pulling fuses and isolated it to fuse #25, the GEM system fuse(with relay #1 still removed). When I pulled this fuse I could hear another relay in the dash(next to the radio) click. With the fuse in place and relay #1 still removed my current draw would go from .5A to 0 when I pulled this relay. I had a few extra relays and tried them but nothing worked.
The biggest problem with the dome light staying on is a switch in the door latch that sticks on...try spraying WD-40 with a spray tube into the latch in the door-that should do the trick. Most Ranger owners have had this problem one time or another....a few other Ranger owners can chime in on this, unless you really do have an electrical problem that some of the guys can help out with.... Just my two-cents.
As mentioned, 99% of the time the problem can be remedied by spraying wd40 on the switch mechanism, which frees up the switch. Spray liberally and work the door handle while spraying. If that doesn't work then the switch probably bad and has to be replaced.