My son is building a 1981 Z28 that he purchased. The engine had been replaced and all the emissions and smog controls had been removed when he purchased it. We are in the process of replacing the engine and have no plans to reinstall any of the emissions or smog controls. Our problem is the gauges (tach, temp, volts) on the dash don't work. We found the computer has been removed and the harness cut at the firewall. The remainder of the harness is still plugged into a connecter coming from the dash area. Could this be the problem with the gauges and is there a way to unplug that harness and put jumpers in so that the gauges work? I've been looking over the wiring diagrams (Haynes and Autozone) but don’t see a link that would cause the problem except for the check engine light. I'm new here and may be posting in the wrong area. If so, let me know. Any help would be appreciated.

I posted this in the V8 Tech section and got no response so I'm trying here.

 

Welcome!
The simplest way to fix the problems is to just remove the gauge cluster and fit new gauges to the existing locations, or to a new gauge insert like a Covan. By the time you got all the correct sending units to work with factory gauges, then the frustration of sorting out the wires at the block, you'd be driving around with your new gauges, and not spend as much time or money.
Besides it will look way tricker too!