I have a 99 XJ that used to be owned by the state. There’s a black screw on plug on the back of the vehicle. There’s a bolt sticking up through the roof in the front where I think another plug is supposed to go.

Im guessing this was for a single bulb hazard light; kind of like those green USPS mail jeeps.
Anyways, water makes its way into the car because there’s no gasket/plug on the front one.

Anyone know where I can get one or what they are called?

 

IDK what they are called, but back in the days of CB radio, you could get those plugs at Radio Shack to repair holes drilled in the roof for antennas. Basically they were like a drywall toggle bolt with a gasket on it.