Dual gas tank switch

[Squinko]

I have a 1975 C20 with dual tanks I recently bought. The switch for the tanks is under the drivers side front seat. In it's current position in the photo it is running off the drivers side tank. When I turn the valve to use the passenger side tank it won't get gas. The value will turn all the way around so I am not sure what position it should be in for the passenger side to work. I tried turning it opposite from where it is and that didn't work. Could be the value isn't working right but I was told both tanks work. It's probably me not knowing what I am doing and where the switch should be.

Any suggestions would be greatly appreciated. Yes both tanks have fuel.
View media item 9611

 

[75gmck25]

That is an aftermarket switch of unknown brand, so I don't know what might be wrong. The OEM switch was a black rocker switch mounted on the dash. I assume you have dealer-added auxiliary tank and switch. The only thing that's odd is that in 1975 the primary tank would have been on the passenger side. When the switch or solenoid fails, it usually runs only off the passenger side tank.

Factory dash switch was a dual-pole, dual throw switch that switched power for the fuel solenoid (under the truck) with one set of poles, and switched the sending unit wire with the other set of poles. Factory fuel solenoid defaulted to the passenger side tank with no power, and when switched to Aux it applied 12 volts to the solenoid and switched it to the driver's side tank. If your truck had fuel return lines it will have a six port solenoid (it switches both fuel and return lines), but with no fuel return line you only needed a 3 port solenoid.

Bruce

 

[Squinko]

That is an aftermarket switch of unknown brand, so I don't know what might be wrong. The OEM switch was a black rocker switch mounted on the dash. I assume you have dealer-added auxiliary tank and switch. The only thing that's odd is that in 1975 the primary tank would have been on the passenger side. When the switch or solenoid fails, it usually runs only off the passenger side tank.

Factory dash switch was a dual-pole, dual throw switch that switched power for the fuel solenoid (under the truck) with one set of poles, and switched the sending unit wire with the other set of poles. Factory fuel solenoid defaulted to the passenger side tank with no power, and when switched to Aux it applied 12 volts to the solenoid and switched it to the driver's side tank. If your truck had fuel return lines it will have a six port solenoid (it switches both fuel and return lines), but with no fuel return line you only needed a 3 port solenoid.

Bruce

Thanks for the info. I guess I will play around with it and see if I can get it to work right.

 

[wanderinthru]

Have you checked for a broken like between the tank and switch?

 

[dsteelejr]

I second everything @75gmck25 said.

I had the same kind of fuel tank switchover valve in my ‘80 K25. My grandfather put it in when he installed a second fuel tank on the driver side in the late 80’s. The switch was wearing out and I’d smell gas when I switched over and the last few times I switched tanks my hand got wet with leaking gas. Decided it was time to change it out. Can’t say for sure what the issue is in your square. Just making the point that these switchover valves do wear out with time. I replaced it with an electric switchover valve like the one @75gmck25 desribed and couldn’t be happier with it.

My grandfather also installed a toggle switch for the fuel gauge so when you manually switched tanks you also had to flip the toggle switch so the gauge would read the level of the tank you were pulling from. I wired the electric fuel tank switchover valve to the fuel gauge switch now the one switch does both and I don’t use the valve on the floor at all. The parts aren’t too expensive and it wasn’t that hard to do. Eventually I’m going to replace the toggle switch with the black factory style switch on the dash. I’d share pics, but I work away from home in the oilfield. Maybe I’ll post some when I get back home.

https://www.summitracing.com/parts/tnk-sov


https://www.summitracing.com/parts/smp-ds1807

 

[Craig Nedrow]

Here is the correct three port solenoid that goes under the truck, like Bruce was talking about. One wire, two fuel in from each tank, one fuel to the carb or what ever you are running. Local NAPA ordered it, about 50 bucks.

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[Nuckollsr]

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My 87 R1500 came with saddle tanks. Of course, it had the big valve under the bed that switch supply lines, return lines and fuel level senders. I ditched the big valve and plumbed both tanks together through check valves to the TBI carb. The return line is permanently feeding the right tank. The fuel gauge is looking at the left tank all the time.

Protocol calls for running right tank until the engine sputters. Switch to left tank until gauge shows about 1/3 full. Then switch back to right tank to exploit the return fuel until engine sputters again. Then back to left tank with a gauge reminding me that I should not have driven past that last fuel stop!

Minimal plumbing, no gauge switching. Only the fuel pump motors are switched via a single pole, double throw switch on the dash. Attached drawings show before and after the mod. Much simpler wiring and plumbing.

 

[75gmck25]

Wiring is much simpler for the OP’s carbureted ‘75 with mechanical fuel pump. It would have a 3 or 6 port solenoid with a single terminal. The 6 port is for trucks with a fuel return line.