Here is the deal …every time I turn on my A/C blower my tach jumps and the engine starts to run rough then quits. I have disconnected the air compressor thinking that was the problem but nothing changed. The alternator is new and I tested the charging system and the battery, both are fine. Sometimes I can turn on the blower and every thing is fine until I hit a bump then it goes nuts again. Once again the symptoms… when I turn on my A/C blower the tach jumps, speedometer jumps and service engine light flickers (it is on because of a code 36 that I have not fixed yet) I think I have a loose ground or power wire to the ECM but I do not know where they are. Any suggestions? Also when I turn on my wipes the same thing happens but not as bad.

89 Formula 350
350 TPI
Auto
No mods.

 

Yep, definitely a bad ground somewhere. Check for a good connection between the engine and firewall and the engine and the battery.