heater wiring

Here are the air conditioner and heater wiring diagrams click to enlarge the images below and a guide to help you test the connections

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Heater problem
1991 Chevy Truck V8 Four Wheel Drive Manual

we cant get the heater/ac head unit to power up even though there is power there on several wires. we have replaced the wiring harness, computer, selenoids, blower motor, head unit... pretty much everything in the cab that relates to the heater

Is the problem that you are not getting heat or the blower motor doesn't work?