Ok, so I got this all figured out. The space in the fuse panel is for a relay, part number 14014527. According to the guy I talked to at the dealership, it is specific to the 1980 year model, so I guess our 80 model trucks are that unique after all. Be warned that this is a discontinued part!
Here was his explanation. In earlier model trucks if you ran out if fuel on the primary tank (default tank) and switched over to the secondary, as soon as the ignition switch was engaged, it cut the power to the solenoid, which in effect would default back to the empty tank. The solution to the problem was the relay, which explains why there is both a constant power (orange) and a switched power (pink/black). When the pink/black is cut off by use of the ignition switch, the relay switches to the constant power to keep the solenoid engaged into the secondary tank, provided that the switch is in the LH position.
Here is a picture of the relay:
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1980 Chevy K10 Silverado -->
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My wife told me I spent too much time on Facebook. So I bought an old truck. Now she wishes I was on Facebook, it was cheaper.
