1989 E350 with 460 engine.

The high pressure fuel pump under the frame won't start, not getting any voltage. Direct connecting the pump works well. Fuel relay under the hood switches through, but wire disappears in harness and I can't track it. I thus ran a wire direct from the relay to the pump and the truck runs well.

However, before this happened, the pump used to just start up upon turning the ignition key and stopped humming when the car wouldn't start. Is there a pressure switch in the fuel system which might have been the real cause the pump wasn't running before short wiring it? Did I create a safety concern? If there is a pressure switch: where could I find it? Any suggestions are much welcomed.

 

Only if you roll-over and the pump keeps pumping raw fuel into the manifold.

Some cars use a roll-over fuel shutoff , its a safety feature in case the van rolls and is designed to cut the pump off, some put a crankshaft sensor on the transmission, I've seen some on the distributor.
But it would cut power at the pump relay and you still have power there...so..
Back to square 1.

 

I thought all 80s Ford trucks used a safety/fuel cut off switch inside the pass. compartment on the pass. side foot well on the left or right side to cut off the fuel pump in a collision.

On a van it may be inside the trim panel/vent panel on the right hand side near the computer. Basically a black box with a few wires running to it with a white reset button on the top.

I have never seen an EEC system with a fuel pressure cut off switch.

I do not have a wiring schematic in front of me, but, the other thing I would check would be the wiring for the oil pressure switch. If no oil pressure is detected it will cut off the fuel pump in some vehicles.

If this does not help. I suggest posting in the 460 engine forum or ask the same question in the F-series forum as the engines are almost exactly the same except the engine cross member and air cleaner.