More help with dash wiring 1970 C10

[Harrison.]

http://outintheshop.com/faq/wiring/wiring.htm

I'm having a hard time figuring out what the 12/20 gauge pink wires are for. Mine is wired like this, but the engine harness is missing on my truck and will have to be replaced. It's got a 12P coming from the bulkhead, splitting between the fuse panel and the ignition switch. From the fuse panel a 20P wire goes to the cluster connection. The diagram linked shows the 20P is the fuel gauge feed, but how? The wire coming from the fuel gauge is tan.

And what is the 12P supposed to mate to on the engine harness? The diagram shows 20W /OR/ PPL that goes to the starter/coil.

What is this for?