1997 Ford F-250 Fuel gauge, one tank empty, one tank full

At frst I unplugged the sending unit at its electrical plug in connector. I then tried to ground the female end of the plugin to the truck. The key was in the run position. As soon as I unplug the connector the fuel gauge goes all the way full. To avoid this I left it plugged in to keep the tank reading empty and cut the yellow/white wire on the sending unit side of the electrical connction. Then splicing it to another wire and running it to the negative side of the battery the gauge moves all the way past full again. Also, with the key in the run position, I put my test light into the female ends on the wiring harness side of the connectors to test for power, it never lit up on all 4 wires. The truck will run and use the fuel from both tanks. If I unplug the connector and try to start the truck it wont so it must work for the pump. Why do both tanks read all the way past full when the electrical plug in to the sending units is unplugged? Would it have anything to do with the dome light coming onvery time the brakes are pushed?

Here is what I have for the wiring at the front tank.
Sending unit side Wiring harness side
Black Black
Black/PinkRed
Gray/RedOrange
Yellow/WhiteYellow/Blue

With the connector plugged in its empty. With it unplugged its pegged past full. When I press the brakes the dome light comes on and when I open the drivers door the dome light does not come on. Do you think this could all be related? It appears the guy before me had speaker stuff hooked up. I found a cut aftermarket wire run into the fuse panel. Do these systems share the same wiring?

I found the ground under the drivers side tailight. It had 2 white wires to the frame. I cleaned it up and nothing. I replaced the door jamb switch and nothing. The passenger side does work however, always did. The fuel gauges are the same. Im going to bring my meter home tommorow and check the ohms. The dome light still comes on when breaking. It appears to me that the passenger side door jamb switch wiring runs along the dash into the fuse box and then to the drivers side switch. Could a bad gauge do all of this?

Both grounds are good. No keyless entry. No, the door chime doesnt work at any time. Heavy Duty model. After dinner I am going to check ohms. Would a bad tank selector do this?

Ok, I got under the truck with my meter. With the key off I tested the Black and Blue/Yellow wire on the wiring harness side of the midship tank. I got 155 ohms. Then I went from the yellow/white wire to the gas tank as my ground on the midship tank 1494 ohm. I could not produce any results with the rear tank. I tried both the ways as the midship tank and switched the fuel to rear tank, nothing.

OK, we are making progress. I applied voltage to the black/light blue wire and the dome light did come on. The chime did not. Yes, I unplugged the wire harness plug at the sending unit before resistance testing. Im going to search for the broken wire. Im going to guess that the kid before me may have tied his radio stuff into these wires for power?

I have power coming into and going out of fuse #8. I dont see any cuts, splices, or breaks. The fuse panel is directly above the door jamb sensor, the wire cant be that long unless it goes into the instrument cluster? I removed the tank selector switch and jumped the terminals with the same results so it must not be the problem. I have 8 volts at the tank selector. I filled the mid tank this morning on my way to work. Of course it still read E. I dont work far from home and didnt use much fuel. I pulled the truck in the garage to start my wire search tonight and it went to F? The rear tank still nothing. It looks like it may be a legitimate Full, its on the line not past it. What is the deal with this thing?