I bought a 77 K10 a few weeks ago, and decided I want to start fixing it up slowly. The main issue I've been having is a fuel delivery problem, which I think I've solved with a new fuel pump. The fuel gauge does not work, and I think that's the next issue I want to tackle. The truck has dual tanks with a selector switch in the dash to switch between tanks, and I don't get a fuel level reading for either tank. The PO said that the passenger side tank hasn't worked in forever, it's been run only on the driver side tank for years. This morning, I went ahead and dropped the passenger side tank and removed the sending unit. I'm planning on going ahead and picking up two new sending units, and a new fuel selector valve and fixing the junk wiring for them. I know there are two different fuel systems - one with a return line, and one without. When I replaced the fuel pump, the one I removed had only an inlet and an outlet, no third port for a return line. BUT, the truck has two fuel lines running from the engine back to the fuel selector valve, but only the inlet was hooked up. The second line was just disconnected and hanging there Also, I found an old fuel pump in the back of the truck that DID have the return line port. So when I replaced the pump a few days ago, I replaced it with a pump that had the return, and hooked the return line up. Everything is running for the most part. The fuel selector vavle has six ports - I'm assuming that is pressure and return from drivers tank, pressure and return from passenger tank, and then pressure and return from the engine. Can anybody tell me if that is correct? The sending unit i removed from the passenger tank has three ports, but had one of them plugged off with a plastic bolt. Can anybody tell me if I'm right in thinking that one port is vent, one is pressure and one is return? Next is the fuel selector valve. I've looked on LMC Truck, and they make either a 3 port or 6 port valve. 3 port would be for no returns, and 6 would be for returns? Also, from what I've read, the selector valve defaults to passenger side tank in the absence of 12v power, and switches to drivers tank when it DOES get 12v. The valve on my selector valve has only 1 wire going to it, and it grounds to the frame through the valve body. Does this sound correct? If there's only 1 wire, how would the fuel gauge be able to tell the fuel level in two different tanks?