Tachometer Problem
 

1989 S5 Convertible Turbo Swapped
Megasquirt.

Firstly,
My car idles very well and runs well. So I don't think my ignition system is on it's way out.

A few days ago my horn button had a screw drop out of it, I was test fitting a Grant steering wheel and decided I didn't like it last week so I must have not tightened it down all the way when putting the stock wheel back on. Serious PITA to put back together, ended up unplugging the horn and messing around with it for a few minutes, heard the horn relay clicking a few times as I put it back together. That night my alternator was putting out some low votlage so I cleaned up the terminals and saw .01 volt difference between the alternator post and the battery +
Also had my clock die, but now it works fine.

Now after this my tachometer needle bounces around, sees all sorts of rpm, even the redline buzzer goes off when I try to start it now and then.

Removed the Trailing coil, jumpered the black bullet connectors so the tach uses the signal from the leading coil, still does it.

Both coils (leading and trailing) test out correctly the resistance method.

Both are grounded, timing is correct

could the horn relay have burned anything out? I don't think the tachometer wiring runs through the CPU


TLDR:
Worked on horn
Clock/Alternator (voltage output) acted funny, Tachometer danced and Set off redline buzzer
runs fine
alternator output is fine now
clock is fine/bright
coils have correct resistance and work as they should
tachometer still bounces around entire range, even at idle. even with bullet connectors jumpered
what to check now?