any others dome lights.

Are you asking about the dome light that is illuminated when you open the door? Look at the door switch. Common for them to fail.

You aren't likely to find a manual for that unit, if one ever existed in the first place. A service manual for that year Dodge van might be of some use, or not.

a lot of the older headlight switches had a position that when you turned the knob all the way to the left it turned on the dome lights.
if your talking about a bad wire to the ceiling lights of the camper that will be tough to find you may have to try to run a new wire to them.

there should be a switch on the light itself and could also have a wall switch or it could be burnt out bulbs or a blown fuse in the supply line.
if it is a shorted out wire a new one may be able to be pulled through using the old one as a pull wire soldering a new wire to the old one and using it to pull it through the wall.

Too many wires to each dome lamp. Your suggestion about burnt bulb is possible will need to check all.

The headlight switch wil have a click stop at one end and that will keep the dome light off when you want to sit wioth the doors left open.