Re: just did CS130 Alternator upgrade, now factory tach having fits
Check the connection as mentioned above, if that doesn't take care of it use a DVOM and measure AC voltage output in the charging system. A bad rectifier bridge can allow AC voltage to leak into the system, giving you a small offset that wreaks havoc with modern electronics.
99 T/A Daily Driver
67 Camaro Traded for my 98
68 Camaro Street/Strip
98 Camaro Race car Best ET 9.08 @ 152 1.18 60'
Dyno sheets don't win races, see you at the track