Yes and no, '79 came with a Dana 20 transfer case. No 4wd light was used. The yes part is the speedometer unit does have a provision for a light. It was used with a automatic tranny and the Quadratrac transfer case. When lit the spot on the speedo shows E drive.
The switch on the transfer case goes to ground,when you shift to 4wd. The light in the speedo already has 12 volts postive. So the switch sends 12 volts negative to the light. Use a mirror to look at the back of the speedo, there should be a open spot on the bottom, shine a flash light in the hole to check.
You will need a light socket with 2 wires, one for the wire from the switch, the other for 12 volts postive with the key in the run position.
The indicator light will be on the bottom left or right. I forget which one. The other one is for the brake warning light/emergency brake.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.