Found the problem after much difficulty. Used the volt meter to determine the hot wire going to the trailer's hydraulic pump was discontinuous. The wire from the trailer plug in to the pump was ok so it had to be the truck's plugin or the truck wiring. The power in/out through the 7 pole plug on the truck was continuous. I then ran a separate fused hot wire to respective pole on the 7 wire plug and the hydraulic pump came on. So it had to be the truck's hot wire was broken somewhere; but how to find it? When the truck was new the dealer spliced in another 7 wire connection for a camper outlet. So that's where I started. The broken wire was enclosed in protective cover so wasn't readily seen. Had to undo wiring harness, unwrap electrical tape, remove a few tie wraps and expose wiring from protective cover. Only then did I discover the broken wire. The dealer cheaped out and did not use heat shrink crimped connectors. All showed some evidence of corrosion but the hot wire was the worst and there appeared to be pull apart stress on the hot wire connection as it was shorter than the other wires. Anyway I redid all the connections with solder and heat shrink. Good to go now.