72 C20 with an interesting previous owner NL2 aux tank modification

[sloGMC]

My truck has dual saddle tanks and no in-cab tank. It had a double-pole, double-throw switch very much like that one, mounted under the gauge panel, and (still has) a selector valve like that.
The valve is available new from tanksinc.com. Don't know if it's based on a previous GM item. Figured my setup was just something a dealer or other outfitter installed. The wire gauge for the sender signals was like 14 awg -- way too much for just a signal.