batt gauge connection on 72/signal lights

[wade]

hi there!!!!! just registered,great site!!
just picked up a 72 gmc, all original, trying to get all the lights and gauges to work and am having a tough time. when i bought the truck all the lights worked fine, turns, park, tail etc. when i got it home the tail lights dont work, sometimes when i turn the right signal on, the left one blinks! when i turn the headlights on, they work fine but the tail lights dont. sometimes there is a very faint glow from the tail lights but thats it, no brake lights either. I picked up a haynes manual, but the wiring diagrams in there are pretty much useless. any help in this matter would be greatly appreciated.

lastly. does anyone know how to connect a factory battery gauge on the instrument panel? this truck has a hei ignition system installed{dont know if that matters} i looked at the back of the gauge and there are no connections at all. gauge seems to work when tested, i guess my question is, what wires need to come from where to hook up the two points on the back of the gauge?