There is a dedicated tach output of the 7x ICM. You should have been using that instead of the white wire that ran from the ICM to the ECM.
I don't think that killed it however.
Does the tach rise to 200 RPM during cranking and then fall back to zero after cranking?
Does the fuel pump run when you turn the key to on, but before cranking? Does it then turn off two seconds later?
If you just barely bump the starter does the ECM turn on the fuel pump again for two seconds and then turn it off again? If you crank it more than a bump this test is not valid.
Do you have fuel pressure?
Have you tried starting fluid?
What makes you think you don't have spark?
Key on but don't crank. The ECM should turn on the fuel pump relay for two seconds and then it should turn off again. Turn off the heater radio and cruise (it clicks too) You won't hear the first click of the fuel pump relay coming on because of the noise of turning the key. You should hear a motorized noise for two seconds. Go to youtube and search for fuel pump, or try it on a different car if you want to hear the noise. After two seconds the relay should click off and the fuel pump noise should stop.
Note - This test can be repeated but the key needs to remain off for at least 45 seconds for the test to be valid. If off shorter than that the ECM may or may not turn the fuel pump on again.
If you just bump the starter then the ECM when it sees an ignition pulse should again turn on the relay. The fuel pump should make the whirring noise. And two seconds later the fuel pump relay should click off and the fuel pump should stop. This test can be repeated immediately and should give the same results.
Cranking the engine may also turn on the fuel pump via the oil pressure switch. Fieros along with most GM cars were wired this way with the oil pressure switch being a back up to the ECM controlled relay. If you crank it for a bit do not be surprised for the fuel pump to run for maybe as long as a minute after you stop cranking when the oil is cold. It will normally continue to run even if you turn the key to off - for as long as it takes the oil pressure to drop to zero.
What the tach needle does when the key is off is meaningless. Non-powered it may do whatever. When you turn the key to on it most likely will twitch a bit - that is normal. When you crank it the tach should rise to about 200 RPM during cranking and then should fall back to zero when you release the key from start back to run (NOT TO OFF). If not that does primary ignition system suspect. This of course assumes the stock tach was working and you still have it.
If you only have your new tach, does the needle rise to 200 RPM during cranking and then fall back to zero after you release the key?
There is a twisted yellow and purple wire that runs from the ICM to the crank sensor located in the middle of the block. Any chance that connector got pulled or disconnected? Is it still plugged in at the ICM (coil pack base)?
No chance you left the crank pick up connector off or left the power connector off at the ICM?
Do you have power on the pink wire of the two wire ICM plug? Assuming so then do you also have ground on the black wire? Best way to test for these is with a 12v test light if you have one since it puts a load on the circuit. If all you have is a meter try it anyways but remember conditions may change once the circuit is under a load (like trying to start the car).
This is the ignition wiring for the DOHC - The tach output wire is shown - Is that the wire you used to feed your tach? The letters are in very small type on the 6 pin connector
[This message has been edited by phonedawgz (edited 08-04-2014).]