TACH Wiring - Very Strange

I had the same issue with mine when I got it, I turned out to be the coil and ECU was wired wrong when the PO switched to electronic ignition.
So, will it do any damage, or should I re-wire it. It seems to be running fine, although I have a pinging (detonation) problem that I'm currently working on (could the incorrect wiring cause my detonation problem?). It seems to have too much advance under load, and the wrong plugs in it. What Plugs do you suggest I run in my 340 with a mild Purple cam?