'83 280ZXT stops sparking when the engine warms up... bad coil?

 

Could be a bad coil. I have seen coils that failed only above a certain temperature. Then they progressively deteriorate while you're trying to test them to the point where they don't work cold, either. A multimeter test to FSM standards while it's cold and then again after warm-up to failue should nail it down.
Could also be a distrib cap/rotor issue (a crack that opens more as it heats, etc.). Your coil wire could also have a heat sensitive failure/crack in it's core. Warm up the car 'til you get a no-spark failure. Then do a continuity test on the coil wire, while you wiggle it around. Intermittent conductivity/resistance tells you the wire's cracked and degraded inside the insulation. Even if it turns out that the coil is the problem, if the cap, rotor, plugs, and wires haven't been replaced in awhile then just go and do it. Not that expensive and if you don't, they'll fail at the worst possible point. There are some other components it *could* be, but they're less likely and these first few are generally far easier to test.

 

I agree while you are checking change everything to prevent any other problems from popping up. I change my wires every tune up. I have never had a car leave me stranded yet.

Friends dont let friends drive anything but a Z.