Left side frame rail Tan Wire? '74 k10 sb

[RoTuN]

In the process of rewiring I have a tan wire that comes out of the bulkhead conn. at the firewall and travels down the left side frame rail with the 2 wires that go to the fuel meters and the green wire that goes to the tank selector valve. The Tan wire has a connector in it at the x-member and goes right back up the right side frame rail. It was cut and just hanging by one of the previous owners so I have no idea where it should go.
I went to the local strip yard and found a '74 with dual tanks and the same setup for wiring as mine, however that Tan wire was cut and hanging off the right frame rail about where the starter would be.
The wiring schematic shows the splice and the connection to "production fuel gauge".........I don't understand why it would be ran outside the cab, down 1 side, up the other just to go back in the cab to the "production fuel gauge" when the fuel gauge is being fed signal from the meters via the tank switch on the dash.

Anyone have a '74 with dual tanks that has that Tan wire on the rt side frame rail?

[bd]

.........I don't understand why it would be ran outside the cab, down 1 side, up the other just to go back in the cab to the "production fuel gauge" when the fuel gauge is being fed signal from the meters via the tank switch on the dash.

On single tank vehicles the gauge was wired directly to the right tank down the frame rail.  With the addition of the auxiliary tank the gauge wire was rerouted back into the cab to the switch, then out to both tanks.  Since you're rewiring, you can run the gauge directly to the dash switch.

Edit:
It was a matter of assembly line convenience and labor cost.

[RoTuN]

Thank you for the help, I'm feeling pretty dumb about this though. Sounds like this is going to be an "extra" wire from the bulkhead connector down the left frame rail since both tanks have their own wires? I believe there is already a wire to the gauge from the switch.

[bd]

Sounds like this is going to be an "extra" wire from the bulkhead connector down the left frame rail since both tanks have their own wires?  I believe there is already a wire to the gauge from the switch.

Look at the diagram in your original post...

The fuel gauge tan wire (Ckt 30) at the top of the diagram is the wire you found "cut and hanging" along the right frame rail.  In other words, that tan wire is the wire used by the factory to connect the fuel tank meter(s) to the fuel gauge, regardless of whether the truck was equipped with single or dual tanks.  Unless someone previously altered the factory wiring, the fuel gauge is not "redundantly" connected directly to the fuel tank selector switch through an additional dash wire. 

With dual tanks, the factory fuel gauge wire (tan) ran down one frame rail and connected to the dual tank harness (tan, or in some cases orange), which then ran back up the opposite frame rail into the cab and selector switch.  From there the fuel gauge wire split through the selector switch then ran back down the frame rail to each fuel tank sending unit via light blue (Ckt 30B) and tan/white stripe (Ckt 30C).

Since you're in the process of rewiring (unless you need to duplicate the factory harness for judging purposes at truck shows), you can eliminate the 18-gauge (Ckt 30 and Ckt 30A) tan (and/or orange) wires along both frame rails.  Then, reroute the (Ckt 30) tan wire running between the instrument cluster harness plug and the bulkhead connector directly to the selector switch without exiting the cab.  That way you will have only three wires running out to the left tank (light blue), right tank (tan/white), and selector valve (light green).

Has this helped clarify it?

[RoTuN]

Yes, I got it now and thank you for helping to clarify!
What I have done is added a blazer tank to the rear which can be filled from the saddle tanks via a fuel pump and the selector solenoid/valve. Return and supply to the motor is done at the 31 gal. blazer tank. I can use the Tan wire in the harness to send meter signal back into the cab for the 31 gal. tank to another fuel gauge or maybe I will piggyback another selector switch (or 2) so I can use the same gauge to read all 3 tanks.

I thank you again for your help and setting my mind straight.

[bd]

You should memorialize your project with pictures then post it up with some narrative text in Project Posts.   

[RoTuN]

I will, do have plenty of pics before/after, etc. but not much free time lately to sit at the computer. Here's a few pics for now and I'll post a thread in the projects later.

Bought it for $800, running and drove it home. Now it's still stripped down after sandblasting and chassis paint.

[RoTuN]

a few more..









I'll save the rest for the projects thread.

[DustyRusty]

Nice work.  Good photo documentation.