Dual Tank Dashboard Switch

[Iowa Fox]

This is my very first post on this forum. I found it while searching for information on my 1987 V1500 GMC with dual tanks and 5.0 throttle body. The truck has 80K on it and I have owned it since it was a couple of years old.  It doesn't get driven in the rain or snow and nothing has ever been done to it just oil & filter maintenance. Pretty much just like it was new.

I had it out one day and switched back and forth between R & L fuel tanks a couple of times, they were both topped off. When I switched from L to R the truck died. Switched back to L and it fired upbut dies the second I switch it to R. I have a GM service manual, TB Supplement, and wiring diagram. The sevice manuals are really ambiguous for diagnostics. I did check the gray & tan wire on the firewall from the selector switch. With the key on neither terminal will light the test light.

I'm not touching anything untill I get this thing diagnosed. Im not even sure how to get the switch out of the dash, just no access from any direction, I did look at the stickes for the selector switches.

Any experts here on the 1987 with dual tanks and TB fuel injection that might be willing to give an old man a few pointers?

Thanks

[Irish_Alley]

First thing I would do it switch it to the tank that doesn't work. Then go to the fuel pump relay under the hood on the passengers side of the firewall. You will see a 3" redwire with a female end apply 12v to it and if the pump is good it will bypass everything and you should hear the that fuel pump run.

If that doesn't work reach behind the dash and squeeze the top and bottom of the switch and push the switch out from the back to the front