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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: AlabamaLiving on October 15, 2017, 09:33:45 am
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I have 1979 K20 std custom deluxe. I'm installing a dual tank system that did not exist before. I've worked out most of my problems connecting the tanks, switch, and gauge. My final problem is finding new fuel tank sending wire from the tank to the selector switch in the cab. I can't find any for a Chevy truck. Has anyone found where to get a wire harness? Midway Muscle Cars on ebay has a lot of them for late 60's and early 70's chevy cars that have the correct connection, but they haven't responded. Thanks for your help.
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PT197
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Thanks, Just ordered two them.
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FYI - I converted my '75 over to dual tanks using a setup I pulled from the junkyard, and found there are some strange wire routings, apparently so the factory could easily install single or dual tanks. On my truck the primary tank was the right/passenger side. I think by '79 they were using the driver's side as primary, so your wiring may be a mirror of mine.
The setup I pulled uses a double pole, double throw (DPDT) rocker switch that firmly clicks each ways, but in some years they used a push-pull switch, and other years they used a spring-loaded rocker switch.
Single tanks
- The tan sending unit wire from gauge goes through firewall with other wires, along behind the engine, and down frame rail to the passenger side (primary tank) sending unit. With one tank that is all the wiring you need.
For dual tanks
- With dual tanks the gauge sending unit wire (above) does not connect to the passenger side tank, but instead crosses over on under the bed to the other tank, and then up the other frame rail, and then back through a multiplug in the firewall to the dash switch. Yes - it does a complete 360 degree path and comes all the way back to the dash.
- The tan wire from the sending unit of the passenger side (primary) also crosses over under the truck, comes up along the same path on the driver's side and connects to the switch.
- The tan/white sending unit wire from the driver's side runs up the frame rail and to the switch.
Then you have the DPDT switch in the dash. On one half of the switch, the middle terminal is connected to the gauge wire, and each side is connected to a sending unit wire. Now you can switch the gauge from the primary tank (tan connected to tan) to the other (tan connected to tan/white).
The other half of the DPDT switch has 12 volts power on the middle terminal, the 12 volt power wire to the solenoid/switch under the truck on one side, and open on the other side.
Flipping the DPDT switch now changes from one sending unit to the other, and at the same time either powers or turns off the six port solenoid (my solenoid switches both fuel feed and fuel return lines) under the truck.
Bruce
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Thank you Bruce for the info. I'm using a 3-port valve, but I'm having problems finding the right switch. Just ordered another switch that looks like it has the 5-terminal connection you spoke of. For others doing this, this forum has it!
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Here are a few useful links
http://forum.73-87chevytrucks.com/smforum/index.php?topic=9072.0
http://forum.73-87chevytrucks.com/smforum/index.php?topic=23517.0
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My truck originally had a dealer-installed aux tank, and it used a 3 port solenoid to switch between tanks. However, since I had a fuel pump with a return line (a 3 port fuel pump), they just left the return line connected to the main tank.
The problem was that when running off the aux tank, the pump would still return excess fuel to the main tank (since it was the only return line). It took me a while to realize that when switched to the aux tank I was draining the aux, but sometimes also slowly refilling the main tank.
Bruce