Just bought a 1987 F-150 4X4 will only burn the rear tank and runs even with the tank select switch unplugged.

 

Your tank switching valve is probably broke. Do you have fuel injection?

 

Yes it's fuel injected. The switch is good. I did some more troubleshooting today. I jumpered from the battery hot to the plug off the switch and with the engine and key off I could hear the rear tank run and the front didn't. I also drove it with the switch unplugged, it acted like it was running out of fuel but kept going. The other weird wiring thing I didn't get to describing cause my keyboard quit working is in the starting circuit. The red w/ blu stripe wire coming from the clutch safety switch had a wire spliced to it. I cut it and it wouldn't crank so I followed the spliced on wire through the firewall and back along the frame to the vicinity of the hi-press fuel pump where it was crimped to a red w/blu stripe wire that goes into the wiring harness heading toward the engine compartment.

 

there is no electrically operated valve on the 87 it uses what Ford calls a "dual function reservoir assembly" that works off the pressure from the in tank pumps to do the return line switching

 

That's what I meant when I said "switching valve". Not the electrical switch.

 

Hay Buddy, I'm having the same problem in my fuel pumps. I'ld like to ride this one out with you if you don't mind.

Joey

 

This thread was back in January. Hopefully he found the problem by now.

 

When I bought my 1990 truck, the previous owner had the front tank hotwired. The rear tank did not work.
I found that the plastic connector in the switch was getting hot and melted the connector.
When that happened, it would loose power to the pump.
I repaired the wiring so both tanks work. But the connector still gets hot and has melted the connector I put in. I am now looking for a new part instead of a used part.
It sounds to me like you might have the same problem.