fuel pump wiring

[1stTurboGN]

Does anyone have a wiring diagram for the fuel pump in an 87 GN? If you could send it to me it would be appreciated. Just got my first GN the other day and was making an attempt to fix the gas guage, so i dropped the tank and the rheostat is toasted and it looks that the previous owner had done some "modifications" to the wiring that may have caused this to happen. Also, none of the auto parts stores have any listings for a complete sending unit, let alone a rheostat, so can anyone tell me if there is any other vehicle sending unit that has the same rheostat that would be available at the parts store? Thanks for your help in advance. -Matt

 

[2QUIK6]

May have to go to the dealer and see if they can look up an equivalent one if they do not stock them still not sure.
My main reason for responding is about the "wiring modifications" you mention and the fact you are new to the TR community...welcome.
The wiring mods, can you describe them more, one of the most popular and beneficial mods is to "hotwire" the fuel pump, this involves a new relay mounted somewhere near the factory weatherpack harness where the fuel pump wires plug together, from that new relay, there will be a heavy gauge wire that will run from the relay to the altenator, this is the new power to the pump because the original factory wiring was light gauge and would loose voltage when the pump was working hardest, the original power wire in this new configuration simply turns "on" the relay to allow the new heavy gauge wire to power the pump directly from the source/altenator with very little drop in voltage as demand goes up.
If this appears to be what you have, don't remove it, its a good thing.
Now, while you have the pump assembly out, if you don't know how old your fuel pump is, now is a good time to replace it with a new Walbro unit and a new clean fuel pickup sock that snaps on the end of the pump.
Also, look and see if the factory resonator has been replaced with a rubber hose, it will be between the pump outlet and the steel fuel line, about 2 inches there, usually when the pump is replaced, the stock resonator is tossed and replaced with a piece of hose there.
Another good idea is to cut the tip of the steel fuel line at this point, if you look at it, you'll notice it necks down smaller than the rest of the fuel line where the resonator or rubber hose connects to it from the pump, this is a restriction to the entire flow as that is the smallest part, cut off the small part, being sure not to leave any burrs that can rupture the rubber hose that you'll need to connect there from the pump.

Didn't mean to get you off topic, but thought I'd share that info with you while you have the tank down.

 

[1stTurboGN]

I looked at the wiring a little better last night and the pump was hotwired like you suspected. the factory plug had 3 wires coming out of it.... the black going directly to the pump assembly, the greenish one in the middle was cut and looped back for a kill switch and the third one was just cut and replaced with the large gauge wire to the alternator. I have yet to find the relay its connected to, but ill keep looking. It looks like the other mods to the fuel pump you were talking about have already been done so i am hoping the pump is newer cause im low on funding for a new one. Aaaaand as for the rheostat, my search for that will have to wait till tomorrow on account of i just realized its easter Sunday and everyone is at church or out chewin chocolate. thaks for your help!!!

 

[2QUIK6]

Here's a pic of my fuel pump wiring at the rear bumper:
http://hometown.aol.com/onebadwskier/images/Fuel-pump-wiring.jpg

The relay is the box on the bottom right with the single large wire going off at the bottom left.
The 3-wire weather pack on the left is the wires to the pump, the 3-wire pack at the top right is the original source.
Notice only the gray wire goes to the new relay, and it is replaced by the large red wire going to the pump 3-wire pack. There is also a common ground that goes from the relay to the pump 3-wire pack tied in with the original ground (black wire).

It's the "gray" wire that when it becomes "hot", it triggers the relay to allow power to flow from the big red wire which connects to the altenator, to the fuel pump...so the gray wire turns on and off the pump.
Somewhere that big wire to your altenator has to have a relay on it otherwise your pump would run 24/7, unless someone wired in a manual switch, but you'd have to turn it on and off everytime you started the car.

 

[1stTurboGN]

OK, first off, thanks for all the help and time spent taking pics and so on 2quik6. Th relay used is mounted on the drivers side under the hood. off of the factory harness in the back the black was ground, the guy ran the purple wire to the kill switch which does absolutely nothing but make the gauge not work when it is off, and the grey wire was just cut and used for nothing, which makes me wonder what is being used to trigger the relay. Another day, another wire to trace. thanks again!

 

[2QUIK6]

If the relay is mounted up under the hood, there's a wire coming out of the harness right behind and below the altenator that has a connector that is not connected to anything, I think its a brown connector...anyway, that is connected to the fp power, could be using that for the relay trigger...I use it to empty my tank by connecting a wire to the empty connector and the altenator post when the car is not running with the schrader valve removed.