As far as the black knob, that is not what my dad had. Most likely there should have been a switch in the controls for the heater, when it was stock. It is possible that they just connected the wire to ground and it gets power when the switch is on, but the other end is not running to the tanks. Since the truck runs out of fuel after you flip the switch, the solenoid is getting stuck in between tanks most likely. This would mean that you should bypass the solenoid, and connect directly to the line that feeds the engine. This will allow you to run one tank. The solenoids are relatively cheap to replace, but it isn't going to fix the guage. Looking at that picture, it looks like the right side of the heater controls has the switch still there. If that is the case, look for the yellow wires (I believe) that feed into that. There should be at least two, but I don't know if the one feeding the guage will be the same color, and try and ground out the wires there, until the guage jumps. Then it would be a simple matter of having a switch that could swap the two tanks for the guage. Hope this helps a little
...anyone elce wanna gimme a hint on this...im still kinda lost on it..
