They are relatively easy to install.. although I'm not familiar with the terminator. On a Mopar Crate Harness, it's super easy, as it uses star connectors. If Holley uses them, piece of cake. Otherwise you need to tap into can for throttle signal etc. Russel will point you in the right direction. There are only a few required wires to run.. constant power, keyed power, ground, brake +12 volt output, clutch interlock or neutral safety (just ran mine to ground) and as I said, I run MCH so I just plugged into the star connector. Plug in the shifter and start driving. There are opptional wires that you can add into the harness (easy pre terminaled wires that you just pin into connector) such as speedo, reverse light trigger for relay, sport and track mode etc.
