If I remember right, the 7.3 glow plug controller has a black wire that is grounded to the block or other metallic ground, and a small 10mm(I think) terminal which needs a key on hot or manually switched direct 12V. The 2 fusible links which form the glow plug harness bolt onto the larger bolt at the base of the zigzag metallic part of the controller, which is the relay. DON"T put constant or key on voltage at the base of the relay, this will fry your glow plugs. There is a diagram somewhere on here search under solid state conversions or something. FYI I used a 16 AWG wire to the red terminal of the GP controller and spliced that into the red key on hot wire going to the fuel shutoff solenoid on my IP. I don't know if you want to do that or not since it is kind of redneck.