I have an 87 chevy truck. It has the dual tanks. The problems began when the truck would run on one tank, and I couldn't switch to the other, and vice versa. finally the truck would not start, fuel gauge was dead reading half fuel. I have replaced the fuel selector valve along pax side frame rail. The selector switch has no power to it. I have traced the wiring down and if I put 12V between the orange wire(in the fuel pump relay) and the wire going to the selector switch. The fuel guage works and I can hear the fuel selector valve clicking, but truck will not start. The wiring diagram I have in the haynes manual does not show dual tank installation. I have replaced the fuel tank switch, fuel pump relay, fuel tank selector valve, and ECM computer, fuses look good. Need help guys, trucks been down for a week!!!