Tank sending units
 

I am gathering parts to replace my entire fuel system tanks,tank sensors.switching valve and dash switch. I have an '86 body and a '74 frame. the switching valve is a 6 port so I bought one of those ACDelco U7001 and 1 tank sensing unit ACDelco FLS 1001 from Summit which is the only AC one they list. Question: I see on Amazon there is a FLS 1002 which they say is for an auxilery tank. What's w/that? Would the FLS 1001 work on either tank? Also am getting the ACDelco D7089C switch which is recommended and it supposed to plug right in the existing wiring. The truck now is on the passenger side default tank,gauge works. Me thinks I have shorted a green wire to the manifold and maybe smoked the switching valve. I did replace the dash switch with another like one which has the Depress Fully printed on the bottom,no change.I just changed heads and cam and can do stuff like that but I find this fuel electrical a little complicated for me.
A little feed back please,Thank you.

Re: Tank sending units
 

The fuel sending units are not interchangeable, or at least aren't intended to be. When installed into older carbureted tanks with no baffles, they might be interchangeable. In a TBI tank, the sending unit won't set in the basket correctly. Also, the external lines are longer on the passenger side, for some reason.

GM called one tank the primary, and the other tank the auxiliary. To confuse things, it appears that GM changed which tank was the designated primary in the late 70's.

Regardless, if you order one of each sending unit, you should have a set.

Re: Tank sending units
 

The DEPRESS FULLY switch is a momentary contact switch that springs back to OFF as soon as you let go of the switch.
I can't see how you could damage the motor in the valve.
It's a DC motor that spins different directions based on the polarity of terminals D & E.

The Dual Tank Theory of operation writeup may help clear things up for you. You have the 81-91 system in post #2.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

Re: Tank sending units
 

Is there any harm in using a different switch? I just redid my entire fuel system, converting from the old style selector valve to the new style. But the switch i used has no OFF position, it’s ON-ON. I’m guessing the difference is that instead of the new valve only being powered for a second or so during switching, my valve is always getting power. Is that a bad thing?

Re: Tank sending units
 

You can use the 87-91 TBI switch I mentioned in the theory of operation thread.
Some of them have the locator lump on a different terminal than the Momentary switch so you'll need to modify the plastic connector shell for the locator lump on the TBI switch terminal.