fuel pump ?'s

[kmanrsss]

long story short i have swapped cabs onto my 87 V20. got it running the other day but haven't figured out a few things. when the key is turned to the on position the drivers side fuel pump runs constantly. I'm under the assumption that it should only run for a few seconds before the truck starts, then run constantly. The tank selector valve doesn't change tanks when the switch in the cab is pressed, switch is new. ive got another valve that when power is jumped to the terminals it sounds like it swaps over but not when the wiring harness is plugged into it. Im thinking they are somehow related. looking for some direction, and thinking out loud. funny thing is before the swap only the pass. side tank worked.

[bd]

Wiring for your dual tank system...
http://forum.73-87chevytrucks.com/smforum/index.php/topic,9072.msg60580.html#msg60580

Has anyone been creative with the wiring?  When you swapped cabs, did you keep the 87 selector switch?  To determine if you have a fuel module, what engine & GVWR?  What happens if you unplug the fuel pump relay?

[kmanrsss]

The wiring seems original. Nothing obvious at this point. I changed out the 87 selector switch and wiring as it was different then the 83's along with all the other harnesses. There is a fuel module that I don't believe was plugged in when I took the truck apart as it wasn't labeled, but I found the corresponding plug for it and plugged it in. It's got LB7 brakes so I believe that's the 85-8800 gvw range. I'll look into removing the relay tomorrow night or this weekend. Would the module have anything to do with the constant run?

[kmanrsss]

Sorry, that should be JB7 brakes. LB7 is a Duramax motor.

[bd]

You might have a faulty fuel module.  Unplug the fuel module and see if the fuel pump stops running.  If it continues to run, unplug the fuel pump relay.  If it still continues to run, w/o plugging in the relay, unplug the oil pressure switch (org & brn wires) next to the distributor.  Let us know.  Do you have a test light and DVOM?

[kmanrsss]

I'll try those tonight. Yup I've got both test light and meter

[kmanrsss]

I disconnected the fuel module and the pump runs for 3 sec and stops. The truck starts and runs for a few min so I'm assuming the pump is running. Still open headers so I can't hear the pump. I've got no power at the selector switch. At what point should I have power there? I get power if I back feed the pump prime circuit. I have not checked with the truck running as I was called in for dinner. Thanks

[kmanrsss]

Got power at the switch with truck running. Just gotta keep tracing it down.

[kmanrsss]

Got it figured out. Turns out I'm a moron. Gotta plug in all the connectors to get power to the tanks/pumps