[hatzie]

Originally Posted by 78trk

I have a 78 with 2 tanks. I used a switch and wiring connector for a 81-87 w/carb. from Chevrolet. The after market switches seem to come apart to easy. Enlarge the hole for newer style switch and add a ground wire to switch.
I used a 81-87 6 port fuel tank switch.
I used the existing hot wire to the input of the old switch and that switched one tank on the fuel tank valve and I added another wire to the output of the switch to switch the other tank on the valve.
I attached the gas tank sensor wires to the fuel tank valve.
The new momentary fuel tank valve is a much better valve and after the dash switch switches tanks it shuts off power to the valve.

The Delco Momentary rocker switch is a pain in the neck and there's no reason for it. Use a maintained state switch. The valve shuts off power to itself using diodes on the internal limit switch.
Cole Hersee makes an excellent quality polarity reversing toggle switch. http://www.colehersee.com/home/item/cat/52/55018-01/
It's far more robust than the 81-86 or 87-91 AC Delco polarity reversing rockers. You could re-use the 74-80 switch connector on it, that's actually still produced, instead of searching for the long obsolete 81-91 switch connector. A toggle will mount like Ray did at the bottom of the lip on the dash.

One could keep the rocker for the gauge and put the valve toggle right next to it. It would allow a check of fuel levels without swapping the run tank.

There are lots of ways to do this. The relay arrangement was me staying away from heavy modifications to the existing harness.