Chassis Harness

[1991GMCshortstepside]

Questions for those doing stand alone engine harness. I’m trying to run aftermarket gauges, oem steering column, oem ac controls. I have a 91 C1500 with an ls swap. Is the stock ecu/pcm needed for the ac/heater to work? Is it easier to buy a new chassis harness? What manufacturer should I go with for a new harness? The standalone works just fine, but I bought a rebuilt steering column, tried to salvage chassis harness out of two trucks. It’s not working out. Head lights work, no blinkers, no tail lights, no interior lights, no power to inside cab, no Ac. Any advice is appreciated.

 

[gearheadE30]

Been a while since I looked at the diagrams when I did my standalone (in an '89) but I remember the body and engine harnesses being separate. None of the interior stuff requires the ECM harness to work except the AC wiring, but that is a signal from the dash to the ECM and AC compressor so shouldn't impact anything else. From what you said, I'd be starting with the fuse box/power distribution under the dash and making sure that it's making it into the interior. Likely will just be a lot of time spent with a meter and a wiring diagram; it's hard to diagnose non-stock electronics remotely.

As an alternative...there are always GMT400s in junkyards. Might be possible to grab a complete unmolested harness and work from there.