Installed new coil, now the tach acts funny
Righty if it is not system electrical noise cause by something such as the charging system, the only thing left is "something odd" going on with the ignition box. I would try to find SOMETHING to substitute, such as a working junkyard Mopar ECU or a GM module which you could easily "rig" if nothing else temporarily. This is my "infamous" emergency ignition---a coil, an GM 4 pin, to clip leads, and a Mopar dist. connector
This circuit, nicely drawn by a great member here
in this box
Righty if it is not system electrical noise cause by something such as the charging system, the only thing left is "something odd" going on with the ignition box. I would try to find SOMETHING to substitute, such as a working junkyard Mopar ECU or a GM module which you could easily "rig" if nothing else temporarily. This is my "infamous" emergency ignition---a coil, an GM 4 pin, to clip leads, and a Mopar dist. connector
This circuit, nicely drawn by a great member here
in this box