Oops. Probably shouldn't have done that.

Somewittyusername · May 2, 2024

So looking for a little help here. My ride has been a wiring nightmare since I bought it but that's besides the point. After doing some wiring on the NSS I had the bright idea of unplugging the 5 pin fuel switch under the dash as I repainted another to replace it with. Not thinking through that that would shut off my main as well. The truck only has one tank so my thinking is I could just eliminate all the wires a side from 2 or 3 going to the main? I've looked and haven't found a good source for what color is what and how it should be connected. I do have a "Eh" quality picture of the plug before I ripped it apart. And a pic of some of the loose ended wires under the dash. She may not run but at least I've got reverse/backup lights now right?

Ricko1966 · May 2, 2024

Did the truck use to have dual tanks? Is it the dual tank switch that you are referring to?What year is the truck? If you are trying to bypass a switch, using your ohm meter on the switch. See which terminals show zero resistance and infinite resistance as you switch the switch. Look at the pins on the switch that will tell you what wires to connect. After we knowbyear and what switch you are talking about,maybe someone will know which color wires to connect. Good luck.

Somewittyusername · May 2, 2024

Ricko1966 said:
Did the truck use to have dual tanks? Is it the dual tank switch that you are referring to?What year is the truck? If you are trying to bypass a switch, using your ohm meter on the switch. See which terminals show zero resistance and infinite resistance as you switch the switch. Look at the pins on the switch that will tell you what wires to connect. After we knowbyear and what switch you are talking about,maybe someone will know which color wires to connect. Good luck.

Oh sorry. Its a 79. Im assuming it used to have duals with a different bed. But went to one with the bed swap from PO. The switch is what I posted. Nothing marked. 2 position switch. Aux and Main haven't tested ohms yet. Hoping someone would recognize the color coding.

Ricko1966 · May 2, 2024

I'm looking for a decent wiring diaghram for a 79. How many wires total go to that switch?

Ricko1966 · May 2, 2024

Is it a 6 wire switch? The center 2 will be independent of each other and each center will switch to the pin above or below it. I'm not having any luck finding a wiring diaghram. I'd just check with an ohmmeter. Do yoi know how to check a switch with an ohm meter,? If not I can walk you through it. If so I don't want to type a novel in this post.

Somewittyusername · May 2, 2024

Ricko1966 said:
I'm looking for a decent wiring diaghram for a 79. How many wires total go to that switch?

Im not sure. The ones plugged in the second photo were me trying to get them back in order. The first pic is of it originally before I oopsed. The switch has 5 pins. One corner is not there. Thats the way it was.

Ricko1966 · May 2, 2024

If the wires aren't in the original locations then ohm meter doesn't help. I can't tell what's hooked where in your first pic.

Jgonick · May 2, 2024

I don't know if this will help, but here is 79 dual tanks wiring

Somewittyusername · May 2, 2024

Jgonick said:
I don't know if this will help, but here is 79 dual tanks wiring

That is pretty close to what I'm looking for. However, I have a red red wire so I'm wondering if something has been messed with. This. Will give me a good starting point though. Thank you very much!

Grit dog · May 5, 2024

@Somewittyusername, what you have is not OE GM, but had an aftermarket aux fuel tank at some point.
That may not match up with OE wiring schematic for dual tanks.
Haven’t dug into mine yet, because it all works, so idk. But my 77 is oe single tank with aftermarket aux tank. Has a 1 wire switching solenoid underneath and a 3 port valve (no return lines).
IMO you’d be better off following a single tank wiring diagram and matching the wires from the sender to the gauge. Pretty sure you can abandon anything to do with the aux tank.

SlickGTP · May 20, 2024

If you only have one tank installed, you could just eliminate the solenoid and just install hoses from the existing tank to the fuel lines going up to the pump. Minimizes failure points and simplifies life on the whole.

I went the other route and installed a factory aux tank and complicated my life.

Is nice having the extra 20 gallons though.

dsteelejr · May 29, 2024

If I understand correctly, you have one fuel tank and a wiring that goes through a switch for dual tanks that no longer exist? I’m not sure what you meant by shut off your main as well.

If you’re sticking to the single tank setup then you only need one wire from the fuel gauge to the sending unit in the tank. On the back of the instrument cluster plug there’s a pink wire, circuit #30 on the wiring diagram, that runs from the instrument cluster plug to the bulkhead connector, which passes through the fire wall. From there the wire runs down to the fuel tank sending unit. That’s all you need. Route and splice the pink wire from the cluster plug to the pink #30 wire at the bulkhead connector. Delete everything else.

Oops. Probably shouldn't have done that.

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