Won't switch tanks...
Hotshot
Joined: Jun 2007
Posts: 10,008
Likes: 7
From: Austin, TX
It could be the switch, the selector valve on the frame, or the wiring going to the selector valve. When you switch tanks, does the fuel gauge go up or down to the correct level that the tank you switched to? If so I would assume that the switch is good and check voltage when you switch tanks at the selector valve. If the wiring is good and the switch is good, the selector valve probably needs to be changed. Mine does this off and on. Sometimes it won't switch tanks and if I switch it back and forth a few times it will usually go ahead and switch.
Hotshot
Joined: Jun 2007
Posts: 10,008
Likes: 7
From: Austin, TX
Does the fuel gauge work on the tank that works? If the gauge just doesn't work on either tank, I think fuse #6 is for the fuel selector switch and the gauge. I would have to check that though.
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Postmaster
Joined: Sep 2007
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From: Medford Oregon
Cab fuel tank switch only controls the motor inside the selector valve module mounted on the frame, nothing else The motor in there also controls a set of switches which controls which fuel sending unit is active.
As Travis indicated under dash fuse #6 protects that motor and also the AC clutch, best I can determine. I would check the fuse first as the cab tank switch seldom fails ... unless you or someone else have been messing around with the dash and the harness is loose - unplugged from the switch.
Does the AC compressor work; if not check the fuse.
As Travis indicated under dash fuse #6 protects that motor and also the AC clutch, best I can determine. I would check the fuse first as the cab tank switch seldom fails ... unless you or someone else have been messing around with the dash and the harness is loose - unplugged from the switch.
Does the AC compressor work; if not check the fuse.
Logistics Pro
Joined: Oct 2008
Posts: 4,818
Likes: 1
From: Avilla, IN
Have you ever tore apart a selector valve? There is a little electric motor in there that turns a screw. The screw causes a unit to move laterally inside the housing that has two functions. First, the unit's motion operates a plunger that slides past the fittings that go to each tank, blocking off one tank at a time. Secondly, the unit has electrical connections on it that move with the unit. In one position it is connected to the wire the goes to the fuel level sensor for that tank. When you flip the switch the motor turns and the unit moves, switching which tank the fuel is drawn from, and which fuel level sensor is connected to the gauge. This is why there are five wires on the harness. I could get some pictures if you want.
So just because the gauge doesn't switch doesn't mean the switch is bad. It just means that the unit inside the selector valve isn't moving like it is supposed to.
So just because the gauge doesn't switch doesn't mean the switch is bad. It just means that the unit inside the selector valve isn't moving like it is supposed to.
FOREIGN GURU
Joined: Jul 2006
Posts: 7,655
Likes: 7
From: Celaya, Gto. MX
Have you ever tore apart a selector valve? There is a little electric motor in there that turns a screw. The screw causes a unit to move laterally inside the housing that has two functions. First, the unit's motion operates a plunger that slides past the fittings that go to each tank, blocking off one tank at a time. Secondly, the unit has electrical connections on it that move with the unit. In one position it is connected to the wire the goes to the fuel level sensor for that tank. When you flip the switch the motor turns and the unit moves, switching which tank the fuel is drawn from, and which fuel level sensor is connected to the gauge. This is why there are five wires on the harness. I could get some pictures if you want.
So just because the gauge doesn't switch doesn't mean the switch is bad. It just means that the unit inside the selector valve isn't moving like it is supposed to.
So just because the gauge doesn't switch doesn't mean the switch is bad. It just means that the unit inside the selector valve isn't moving like it is supposed to.
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
Well it also must switch the return line as well, right? So the supply, return and sending unit switching is all done in the same gizmo? (Yeah, I never looked that closely when I was under there.