dual tank with TBI issue

[KazuyaIB]

Well im having an issue with getting the dual tanks to work on my new tbi set up. I've got everything rigged up except knowing where to connect this one solely wire that my 91 wiring harness does not have.(since the dual tank wiring for TBI came from an 87). I'l show some pictures to let ya know what i mean.


Here is the wiring itself and the wire im referring to is the one right outside of the Grommet.



This is the exact wire which is tan looking and on the 87 went to the fuse box through the outside. My 91 wiring does not have that wire that goes to the fuse box and do not know where to exactly hook it up. Any suggestions to where exactly i can hook it up to. If you need more pictures or information let me know.

[TravisMartin]

First off, take a look at this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=368431
one of the members was kind enough to post a scan of the relevant wiring diagram.

Unfortunately, it doesn't show where the tan wire goes, but I can tell you what it does and that should help you find it...it is the +12 volt supply to the fuel tank changeover switch, supplying the power to move the selector valve to whichever tank you select as well as supplying power to the correct fuel pump in the tank. It should connect to the fuel pump relay that's on the firewall a little to the passenger's side from center, near the air conditioning suitcase. If you have a TH400 transmission, there will be two relays there...the fuel pump relay is the one that has a short red wire with an empty plug on it coming from the bottom (that's to prime the fuel pump if you ever need to...)

See if you can find the tan wire leaving the relay and trace it to where it used to go. It needs to mate with the tan wire you're asking about. Also note that there's a black wire on the interior side of the firewall that needs to be grounded. On my 90 crewcab it plugs on to one of the ground tabs over above the fuse panel, in the vicinity of the headlight switch.

Am I understanding you took the harness from a 91? What body style; did it have dual tanks?

All this can be made to work; hope this helps but if not keep asking and we'll figure it out.

Travis

[KazuyaIB]

The Wiring harness came from a 91 chevy suburban. Let me get this right... I can just hook the 12+v tan wire to the same colored tan on the relay and it should work? My idea was to connect it to the fuse box on the part that says IGN( or ignition) since the wiring for the dual tank before on the carburator had it connected there for the 12+v. Let me know if i can do that and still get the same result as hooking to the Relay. Thx, and i hope i can get it working right

[TravisMartin]

Yep, it really is that simple. The suburban only had one tank so the output from the fuel pump relay went straight to the fuel pump; you need to find that wire and connect it to the tan wire in your dual tank setup.

It would work hooked to the fuse panel, but wouldn't be safe...the fuel pump would run whenever the ignition was on whether the engine was running or not. You want it to be like factory, where the fuel pump relay turns the pump on only when the engine is running or cranking.

Don't forget to ground the black wire.

Travis

[KazuyaIB]

Ok thx, il try it as soon as the wet weather stops over here. The ground is at the correct place behind the gauge cluster on the wall where tons of other grounds are. You wouldn't happen to have a wiring diagram of the fuel pump relay for future reference? Maybe a link in these same forums as you seem to have quick links to related topics already discussed in the forums.

[TravisMartin]

I only had a link to the dual tank setup because another member (desert1957) contributed it to a thread I was responding to. I have the manuals but I don't have a working scanner so can't post it.

The drawing in my 1990 Suburban/CrewCab manual shows the tan wire to actually be a tan/white. It comes off of the fuel pump relay on the terminal labeled "E". Terminal "C" is the short red wire that hangs from the relay; its purpose is to run the pump without the engine running if you want to prime the fuel system or test operation of the pump and selector valve.

Travis