Buy a multimeter. You can't do electrical work without it. You can find a cheap one that will give you ohm's and volts. That's about all you need. And, it doesn't need to be all that precise. The one I have (thanks to my wife) cost almost $400. But until Christmas, I used a 30 year old analog multimeter that didn't cost much. I even received one free with an order from some sort of catalog store a while back...oh yeah it's a cheap thing...but it works.
Larry, you're the best! Those pictures clear things up! Good work!
As for the dark green wire, yeah that probably is the temp sender wire. But it would be nice to be sure. An ohm meter would tell you right away. And, as for the grounds, an ohm meter would tell you if those wires are really grounded. You kind of need to know that because if they've been cut, you're circuit won't work. Those ground wires are gathered into a big splice somewhere in the dash harness. You could put the extra black one in one of the empty slots. But I'm puzzled as to why you have an extra one. That's why an ohm meter would be a very nice thing to have. Don't you know anyone who has one and would show you how to use it and help you a little? It would take about five minutes.
Make sure you've got a black wire for ground on the dash frame. It should be on the dash frame, drivers side, bottom inside. It would have an eyelet with a fastener holding it on.
This site may help you:
http://www.firebirdtransamparts.com/techinfo/harness/harness.htm
