If your 1st Gen came from the factory without roof lights, and you want to install the 1st Gen Industries roof light kit, then you will require this template to know where to drill the holes in your roof.
This template tapes to your roof and shows where both the screw holes, and the wiring harness holes get drilled.
This template will work on 2wd and 4wd 1974-1977 medium duty D400/500/600 trucks, and 1977-1993 2wd and 4wd 100/150, 200/250, and 300/350 trucks.