Thanks JohnC. Yes, I've read quite a bit about the relay and the OPS! Ironically, while these may also cause me trouble, I clearly have a ground problem.
From your response and everything else I've read about the system, I'm inferring that there is nothing "downstream" from the Lift Pump in the circuit except the ground. Is this inference correct? I know it seems obvious, but the wiring in my truck is odd enough that it raises questions. Do standard 3500 pickups ground the Lift Pump immediately to the frame bracket, or do they also send a black wire through the plastic harness, way back behind the tank, to a splice (mine broke) with a white ground wire? I'm guessing I've found a weak point in the ambulance wiring scheme. I can't think of any reason not to ground right at the Lift Pump. Thanks again for responding.
Steve