hi i new on here and also new to hooking up gauges. I have a 1996 pontiac sunfire and i got a battery gauge want to hook up but would like to hook it up to where when i turn headlights on then gauge light comes on and when i start the car the gauge will start working.. If anyone knows how or could help and advice would be nice thanks..

You need

Constant -- Tie on to the thick red wire under the dash going to the key switch. (On the left side of the steering column)
Switched -- Tie on to Pink or White in the same location, whichever is easier.
Ground -- Crimp an eye onto the end of your ground wire and screw it into metal.
Illumination -- There will be two brown wires down under the kick panel/door sill inside a big harness. One of them is on with your lights, test to see which.

Also, make sure you put fuses in line with your constant and switched wires.