bought a aftermarket water temp gauge, no instructions. where do i wire this to? i got the electrical working for the light but i still need the rest wired. is there a basic method to installing this?

Electrical or mechanical?

You need a constant power source for an electrical gauge and only a night-time (headlight switch) source for mechanical.

Mechanical is a pain in the ass since you need an NPT adapter for the fitting they give you, and as far as I have been able to tell, that adapter does not exist. Mine is all wired up and the probe is just hanging in the engine bay. Otherwise you have to drill and tap somewhere near the thermostat to place the probe.

Electrical would replace the stock sender and I can't recall which opne that is exactly off the top of my head.

On a 1G, there is a plug on the back side of the thermo housing. It's almost exactly opposite of the stock guage sender. Pull out plug, screw in new sender, wire it up. ;)
2G, you're screwed. I believe Greddy makes a probe mount that you basically clamp in line on the top radiator hose. I've yet to see one for sale anywhere though...
The wiring is easy. Pos goes to sender, ground goes to ground...