The car now has a new ECU. starts and runs fine (yay) but still nothing from the gauges. No
Temp gauge
Fuel gauge
Voltage gauge
Check engine light
Oil pressure gauge
Tachometer
No warning lights at all
The car runs, blinkers and all lights including dash lights work fine. All the fuses are good under the dash. any ideas where to start looking.

Recheck your GAGE fuse.....

Took a multimeter to all the fuses. I have continuity from post to post on all of em. But I will check and see if it actually gets 12v with acc on, (you just made me think of that so thanks)

Checking for continuity with the key off is a fail. It doesn't work. The load on one side will give you "ground" and the multiple loads on the source side will give you a ground. So even with a blown fuse you will get continuity.

Do this instead - Turn the key on and check each side of the fuse for +12v with the other side of the meter grounded on a bolt that is in metal. It is better to use a 12v test light with an alligator clip if you have one. Easier to see the light, better because it loads the circuit slightly, If you find a fuse with +12 on one side and 0 on the other you have your bad fuse.

btw, the Fiero fuse box is hinged and swings to a vertical position. Find the latch, squeeze it towards the fuse box, push up slightly to take the pressure off and swing it down.

[This message has been edited by phonedawgz (edited 07-31-2016).]

This is also a sign of poor plug connection at the back side of the instrument cluster, not sure which side as I have not gone back in to correct it since it's intermittent. I removed the cluster a few months ago in an attempt to make better contact at the terminal surfaces in the lousy factory connection to clear up the intermittent outer back lights for the odometer which resulted in an intermittent dash. Some times I get nothing at all for a few moments at startup but by the time the sun does it's thing on the car continuity returns on its own or after a bump in the road. It really is a lousy arrangement GM designed where with time the cluster contact terminals start to delaminate and corode from the plastic sheet they are adhered to.

Interesting theory on the continuity test being a faulty check, I'm going to look deeper into that after this gets settled. (I could see how your theory could be true) Unfortunately all fuses checked out and I have ACC switched power on both poles of the GAG fuse. (after the initial check i pulled one by one and tested continuity) I guess my next step is to pull the dash. (Dash hasn't been touched in the last 10 years so I suppose something could be starting to rot away. I'll let you know what I find. If anyone has any more ideas lmk. I can't think of a place besides the back of the cluster that all the individual curcuits could be affected by one fault!

Thanks for all the help so far!!!

Your ECM was fried and you have multiple gauges in the dash that don't work. My guess has been that someone put the battery in backwards and fried both the electronics in the ECM and the dash. Best bet - buy a dash from someone on the MALL section of the forum. You should be able to pick one up for cheap. Try to get the same layout as what you had before.

The radio and the alternator are the only other pieces of electronics that might still need replacing. If the alternator is charging the car and the radio works then that eliminates those pieces.

Putting the battery in backwards shouldn't knock the dash out completely particularly the back lighting along with the simplest of these old style gauges which should work in reverse when that happens I could be wrong. I'm eager to hear what the cause is. There are two instances I've experienced resulting in complete power loss at the dash and that's at the plug into the cluster and a fusible link in the 84 model. It could be coincidental in timing with the other failures. That always complicates diagnosing because it gives the impression two independent problems are linked.