Fuel pump electrical issues


Well-Known Member
Alright a little background. I'm working on a friends 87 GN. It recently started blowing the fuel pump fuse. Since Ive known this car, the pump has turned on with the key and stays on (no priming somebody bypassed it). I found somebody elses rig job from way back when. A wire was spliced into the pink and black wire going into the fuel pump relay and run back through the interior to the trunk where it tied into the tan wire. The new rigged wire was grounding out and causing the fuse to blow. I was hoping that somebody did this to avoid replacing a bad relay but it appears to go much deeper than this.

When the key is on I have 12 volts at the pink black stripe wire at the relay, and also the green and white wire at the relay has 12 volts key on as well. The grey wire has no voltage and the grey fuel pump jumper wire on the drivers side near the valve cover doesn't have voltage either. The oil pressure switch wiring has been checked for any issues and all is well. I have checked out the harness on the left side of the fuse block where I believe there is a goldish colored wire that runs the length of the car back to the trunk connector. This leaves me with trying to figure out why I have no power at the grey wires and where do these run? Any notable problem areas for this wire or where it runs? I hope this post is legible. Thanks!
The gold, hard core wire is the original main pump power wire...
As Dank posted, look at the Vortex info. Lots of "good stuff" there.
Check what you can, and post back...
Thanks guys. I used the Vortex site to figure out the wiring schematic but it was written assuming the wiring hasn't been butchered in the past haha. The blue wire to the relay is only supposed to have 12 volts for 2 seconds for the prime and not have voltage after that until its running, but this one has 12 volts the whole time the key is on. and the grey wire still has none. I put 12 volts to the fuel pump bypass connector on the drivers side and still no pump.
Did you try giving power to the pump straight to the connector just to make sure the pump works? To rule that out then check wiring
Did you try giving power to the pump straight to the connector just to make sure the pump works? To rule that out then check wiring

Yeah the pump doesn't turn on with power to the connector but the pump works. It worked with the rigged up line that turned on with just ignition voltage that originally was bypassing the relay.
Maybe there is something going on with the wires at the oil pressure sending unit?
So a buddy came over today to help out a bit. So the green and white striped wire that comes from pin A1 on the ECM pin does not have voltage at the ECM for 2 seconds or at all from what I can tell. Somehow the same wire has 11 volts at the relay fulltime. I don't see where anybody has hotwired it but who knows. I also have checked for voltage at the wiring harness grey wire that goes through the fire wall and into the fuse box and it was good when running 12 volts from the connector near the drivers side valve cover. I have temporarily decided to bypass the factory relay setup and just use the hotwires relay and trigger it with the voltage at the green and white wire. Should be simple. Well when is voltage not voltage? See the youtube video to see what I mean.
Just an update, the ECM was bad. swapped with a known good one and it primed for 2 seconds and then i was able to start the car and all seems well.
. Should be simple. Well when is voltage not voltage?
It's probably because your digital volt meter ( DVM ) doesn't put a load on the circuit . If you would have checked it with the fuel pump hooked up it probably would have read 0 vdc . That is why test lights work well on automotive circuits , they put a load on the circuit with the illumination of the lamp . It's easy to be fooled by a DVM . Sam