I thought that it would be a good idea to install the engine and transmission wiring harnesses prior to putting the body back on the chassis. It gave me good access to the connectors and I was able to judge the cable lengths to determine possible mounting points for the engine controller, the fuse and relay box and the transmission controller. GM did a great job of labeling all of the cable ends which made the hook up dead simple… all that remains to be done before the engine can be fired up is to run the power and ground cables up to the starter area and run a charge line from the alternator to the battery connector. Also, have to plug in the gas pedal… 21st century drive by wire… 

Engine and Transmission Wiring Harness and Controllers