My 86 se wont start, It all started last night while driving the volt meter started to jump around (so did the oil) the volt meter went low and the red light came on, but after revving the engine it went back up. well now , when I went to start the car I just got a click,click from the starter, so I got my Fluke and got a reading of 12.40 volts from the battery, checked the cables, checked the wires and could find nothing wrong .. so I tried to jump it and that did no good ...
any clues?

Well first just because the battery reads 12.4 dosent mean it will start a engine it also has to be able to crank out amps. The battery might not take a load and be dead. First you are gettin a connection or the starter wont make noise. My bet is that the starter died. Fiero's do kill starters because of exhaust heat.

First of all, 12.4V is a little low for a charged battery so I think your battery is dead. Second, the battery went dead while driving so your problem is probably the alternator. If you have a bad alternator, jump starting won't start the car either if the alternator short circuits. Third, it could be that the starter has died (like Lynx said, it happens a lot with Fieros), but that doesn't explain why your voltmeter did what it did.

a bad ground or batery cable would explain the voltmeter..... check all the cables especially the ground leads for block/body and batery/body.

if you end up replacing the starter replace BOTH batery cables at the same time. Make sure the positive one is properly routed, and heat protected.

Ok, I took the battery out and chcked the cables, and all found the terminals were very corrodied , so I cleaned them and charged the battery up and put it back in the car and it started, I put my Fluke on the battery and got readings from 14.20 to 14.65 this tells me my alt is working .. So I drove the car around the block and no sooner did I pull out of the driveway, did the voltmeter go red, when I got back I tested the battery again and got a reading of 9.45 volts now I think to myself that the alt is not working or I got other problems, Im goning to try to test the alt the way that the haynes book tells you too ... if anyone has any toher suggestion plese say so .. thanks for reading
SwampBat

many auto parts stores can also test the alternator.