Three issues before my rebuilt inspection

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Since I pull my truck right out of the junk yard, it has a junking certificate of a vehicle. Not a original title for registration. In order to register the truck I need to apply for a rebuilt title. This requires a state inspection where everything must work. I have three issues to solve before then

1) no backup lights
2) no working fuel gauge
3) no horn

I have install a new dash harness, tail lamp harness, and fuel gauge wire.

Fuel gauge is pegged way past full and no clue what to do.
The horn I think just needs a new contact spring. (Beeps if I ground contact)
The backup lamps may just need a new switch on the 4-speed trans to fix.