Gas gauge wiring question

[Jarrett Melvin]

Planning on installing saddle tanks on my 87 one ton.

Truck already has a single tank with an in tank pump. The gas gauge don't work.

I want to install saddle tanks with an external fuel pump because I already have two new sending units without pumps on them.

Question is, to wire my gas tank to my gas gauge, can I just cut the plug off the original wiring for the old sending unit and just splice into the original gas gauge wire or will I have to change gauges, run new wires?

My gas gauge is currently not working as it as and I don't wanna dive into it and end up not fixing the problem.

 

[crpntr78]

You are more than likely going to have to install new sending units in the tanks like they were manufactured in 83. As that will be the determining factor for working gas gauge.

 

[Jarrett Melvin]

You are more than likely going to have to install new sending units in the tanks like they were manufactured in 83. As that will be the determining factor for working gas gauge.

I never mentioned, the truck I'm putting the saddle tanks on is an 87 with a TBI and has an in tank pump, the sending unit has 3 wires and plug on it. Ground, gauge and to power the pump I assume

I have two new sending units with no pumps on them. That would be used with a mechanical pump and carb system say. They only have a ground wire and the wire for the gauge.

My question is I guess, can I disregard the 3 wire plug that's on the truck now for the sending unit and just keep the gas gauge wire, and run that wire to my new sending unit for the gas gauge?

 

[75gmck25]

Im not familiar with how the tbi sending unit is wired, but on a single tank carburetor sending unit you have a ground wire that connects to the frame, and a tan sending unit wire running up to the gauge. If your tbi sender has 2 more wires they are probably power and ground for the pump, but I don’t really know.

 

[Jarrett Melvin]

Im not familiar with how the tbi sending unit is wired, but on a single tank carburetor sending unit you have a ground wire that connects to the frame, and a tan sending unit wire running up to the gauge. If your tbi sender has 2 more wires they are probably power and ground for the pump, but I don’t really know.

I was looking into it today, reading some schematics and reading some threads. There's two in the truck side of the plug I'll call it and three on the tank side. From what I can understand, black was ground, pink was gauge or fuel level, and the third was power to the pump.

So I'm gunna try running the pink wire from the gauge into my selector valve and wiring the valve as it should be and see if it works.

 

[Nuckollsr]

There's another option.

I have an 87 R1500 with TBI fuel system that came with pretty rusted saddle tanks and a flaky selector valve. Replaced both tanks and pump/sender assemblies. Ditched the selector valve. Plumbed the two pump output lines together with check valves to feed the carburetor. Wired selector switch to run one pump or the other. Tied sender to left tank only. Plumbed TBI return line to right tank.

I run right tank until engine sputters. Then left tank until down to 1/4 or so full . . . then back to right tank to used up return fuel . . . finally back to left with a gauge to remind me how dumb it was to pass up that last gas station.

No monkey motion selector valve. Simple right-left pump switching. Of course anyone but you driving the truck where contents of both tanks are needed may need some instruction . . . but I don't loan my truck.

 

[eric 87]

There's another option.

I have an 87 R1500 with TBI fuel system that came with pretty rusted saddle tanks and a flaky selector valve. Replaced both tanks and pump/sender assemblies. Ditched the selector valve. Plumbed the two pump output lines together with check valves to feed the carburetor. Wired selector switch to run one pump or the other. Tied sender to left tank only. Plumbed TBI return line to right tank.

I run right tank until engine sputters. Then left tank until down to 1/4 or so full . . . then back to right tank to used up return fuel . . . finally back to left with a gauge to remind me how dumb it was to pass up that last gas station.

No monkey motion selector valve. Simple right-left pump switching. Of course anyone but you driving the truck where contents of both tanks are needed may need some instruction . . . but I don't loan my truck.

I am in the middle of converting my TBI to carb in 87 GMC shortbed. I have everything disassembled right now and thought this is the time to do what wiring I want to do. Originally I was going to go the route of splicing into the former distributor 4 wire plugs purple wire to HEI tach port so the computer got signal and kept fuel pumps running. I have a regulator for the carb and all the other needed parts.
I was thinking of using the TBI set up but really want the computer totally out of the equation. Trying to do similar to what you did. Could you have also run the sending unit gauge wire through the dash switch as well so it got power to whichever tank you were using?
I am not the best at wiring. I would like to get switched power to the pumps through that dash switch but like you also want to have two working gauge for both. I want to not even use the relays or anything from the TBI system. Felt it would be easiest to work on all this before I put the intake and carb and pressure regulator in at the firewall. If I do the wiring now. I suppose getting it back to running should be the focus and do the splice into the purple wire for now but....I like to do it right the first time.
What would you do different?