how do i hook up water-meth injection on a 1982 sigma turbo

[simple]

You can:
Inject water between carby and turbo intake
Inject water right after turbo (pipe above valve cover)
Inject water in to each cylinder separate (you will need 4 nozzles)

From what my limited experience telling me, the best would be to inject some water right after turbo to cool down charge and to inject some water in to each cylinder as well to suppress detonation.

With water quantities, usually suggested to start about 15% water to fuel ratio.
Make sure you tune the engine to water injection as otherwise you will not benefit from it. Treat it like fuel injection, too much or too little is not much good to you. Not to mention that ignition timing and air/fuel ration needs to be adjusted.

Just take your time and read thru the forum. There is a lot of useful info here. You will have to learn basics if you want to do the set up your self.