Cannot get fuel pump to run on pickup

Hi folks,
I have a 1989 nissan pickup that would not start after class one night. I checked to see if the fuel pump was operating, but no gas come through the hose. I measured voltage to the quick connect to the electric pump and the voltage was there. However there was no measured voltage across the pump motor terminals, but there is at the positive terminal to ground. The negative terminal runs to the on board computer. I've replaced the fuel pump and the computer and have the same results. I suspect the lead going to the computer shunts the negative side of the pump to ground if a certain condition is met. Could someone please let me know what that condition might be, whether a sensor or what. The LEDs on the computer are both on, one red, one green. There is continuity from the neg side of the pump to the quick connect terminal line of the computer. Thanks folks, I really appreciate the input.

 

It hard to figure out with out being there, but for a temporary fix . I would use 2 wire fuel pump that supplies about 38psi of pressure, or buy a H.O. one and use a fuel psi regulator. Just wire it in to a wire that is hot when the ignition is on. You might find that this setup is less trouble then the one your truck came with.