So for the OP, I would check the wiring under the hood for the IIRC orange wire on the passenger side. It normally has a fabric sheath around it. My guess is its just hanging somewhere and rubbing on the frame or tub.
In order to run the light off a switch in the dash, like others have done, you would need to find the ground wire behind the speedo for the light. Tap into that wire, and run another up to a switch, then ground the other lug on the switch to a ground point on the dash.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.