Fuel selector valve (harness and plumbing)

[BlackNoma]

I have an '89 f350 4x4. My truck only works on the rear tank. When I first got it not too long ago, I wanted to fix that so looked under the truck and there are 2 selector valves, some extra plumbing, and bastardized wiring harnesses.

I'm going to attempt to get it all fixed this weekend.

Does anyone know what voltage I should be reading from each pin on the harness so I can get that squared away before I pull the bed and rearrange the plumbing?
I know some pins won't have any voltage readings because it's going to the fuel gauge, etc... But if you can help me by letting me know which ones should read what when the switch is in both positions (what changes), that would help so much!

A good picture of stock plumbing would be sweet, but no big deal.

Also, a good way to bench test a selector valve would be sweet also.

 

[BlackNoma]

Bump

 

[franklin2]

The diagram in the link is for a 1986, but I think they are basically the same throughout the years. Look on page 98 in this link.

http://www.garysgaragemahal.com/fuel-tank-selector--gauges1.html

You can see the

yellow/white goes to the gauge in the dash. If you ground and unground this wire, the gauge should swing back and forth full scale with the key in run.

yellow/lightblue goes to the rear sending unit

darkblue/yellow goes to the front tank sending unit. The switching is done by the guts of the valve where there is a switch inside activated by the valve motor.

The red and brown/white go to the motor in the valve. That is wired just like a power window switch. Flip the dash switch one way, you get + on the red, neg on the brown/white. Flip the switch the other way, and the polarity switches on the wires, and that makes the little valve motor run the other way.

 

[BlackNoma]

Franklin2, thank you very much!

So by applying 12v / ground to those 2 pins, I should be able to hear the valve actuate and redirect flow? Then blow on various tubes to find out if it's really working?

Should the tubes for the other tank be completely shut off when the valve is in the other position? Or are they just free flow, but not routed to the engine line?