In short, I damaged something in my car while trying to determine if the Coolant Gauge (which was intermittent) was or wasn't working. I stupidly put voltage where it shouldn't be and now I have to fix it. (It went through the wires for the coolant gauge, and I heard the fuel pump relay turn on when I did that.) Now it seems as though the ECU / PCM does not send the right Fuel / Air mix in. The "Check Engine" light popped up and now the car chokes out, I think the engine's running too rich. I already took the Idle Air Control Valve off to see if the car would run with it off, and although it no longer was choking out, the car still smells like there's unburnt fuel and smoke coming out the exhaust.

I bought a code reader for this Pre-OBD 1 type of computer (it's EEC-IV,) but either the reader doesn't work, or the wires to the ECM are broken (they are in the engine bay after all,) or the ECM doesn't send signals (or a combination if not all three.)

So, that said, should I replace the PCM and will it have the same tune? I did remove it. It reads "ES8F-12A650-Y1A" which is a number that I haven't been able to find anywhere else so far (others ending in X1A exist, but I found zero with Y1A.) The metal casing says "Ford" on it. I looked at NAPA Auto Parts for a good replacement, and there are 12 replacements available, so I'm a bit confused about which one I should get (if any one of them.)

The car, again, is a 1990 Mercury Grand Marquis LS Colony Park Station Wagon with the 5.0 (302) engine. I don't suppose it matters much if at all, but it does not have that Instant Clear Windshield option.