with a simple homemade load bank (volt meter to measure drop at one end of the wire, and apply a few amps of load to it on a button) you can suss out an entire disconnected engine harness in an hour max.

i like a load bank with like a 1 amp, 5 amp, and 10 amp load each with its own button. big stuff like injector supply gets a 5 amp load, little stuff like a maf sensor signal gets a 1 amp load.

if a thin old GM sensor wire is even remotely compromised (like even if it's wiggled itself back into place) a few amps usually cooks the damn thing and there ya go.

i use paper clips as my probes, seem to fit inside the female ecm pins fairly well.