A little help please.

[Baggerjohn]

I have a 67 lwb C-10 with a 292, 5 speed. I don't have back up lights. I tested the switch on the trans and it's good. There are no wires from the switch to the tail lights. Can anyone please tell me what I need to get to have them operational. Thanks.
Another question is that with the 292 and 5 speed, single carb, I get terrible mileage. I don't have a speedometer but I use my old gps for speed. I notice at 2500 rpm, I'm going 68 mph in 5th gear. That sounds great but if I go 20 miles, it goes through a quarter tank. That ain't right. Any suggestions on what I can do to improve mileage? I don't have a camper or haul anything. Any help is appreciated.