Not as bad as PAYING someone to do it! Zu's have a sensible harness, connectors only fit connectors in the appropriate area.
Since your prob seems to be in engine control. you're only concern is in the engine bay and ECM.
Never seen a bad wire harness on an Isuzu, or any ***** horse for that matter, unless some ham-fisted radio, alarm system or fog light installer got there first. Odds are your problem lies elsewhere. Zu's are mostly relay controlled with fuseable backup. Wire insulation is more than adequite too.
Perhaps if you could give more specific HISTORY to what led up to this diagnosis, more of us can help you...Cal