Helping a friend on an old E350, it has a single 40 gal tank at the back. After dropping the tank, found the pump was removed off the sending unit assembly, so the high pressure pump up front was doing all the work.

Also previous owner had an other in line pump near the tank that stopped working. Wiring harness in this area is a bit of a mess. Have the new pump/sending unit installed, tank back up. Removed the extra in line pump. I have the level sensor working.

Question, I have power to the front in line high pressure pump, but having trouble figuring out power to the rear pump. Should both pumps be powered off the same wire ?

 

Well I seem to have misplaced my 88 E150 EVTM. I would think your 89 should be similar to my 88 since my 88 has the high pressure pump along with a low pressure pump in the tank.
Here is a diagram I scanned some time back for duel tanks on a 88 van. It shows both pumps running off the same circuit.

 

thank you!