Basic Wiring Harnesses for 1977-81 Trans Ams It's not unusual to find that the wiring on your project Trans Am has been hacked to pieces or even on fire. Some cars in 1980 and all of them in 1981 used an engine control computer harness in addition to these five. The wiring diagram shows there may a harness without rear defrost switch wiring, but I have not seen one without it. Electrical wiring diagrams - Hitman's Pontiac Trans Am Site Hitman's Pontiac Trans Am Forum » Trans Am Information » Trans Am Tech » Print; Pages:  Go Down. Author Topic: Electrical wiring diagrams (Read 12645 times) 0 Members and 1 Guest are viewing this topic. Virginia I am looking for the engine compartment / reverse light switch / AC and heater controls for a 1978 Auxilary Wiring Harnesses for 1977-81 Trans Ams A typical person restoring a Trans Am will want to add and remove options to suit his personal taste. For this reason, as we dismantle Trans Ams, we remove a lot of options and associated optional wiring for sale on eBay. Most of our cars are 1977-81 vintage, and these cars tend to be highly optioned.