Erratic tach and voltage gauges..maybe others?

Alumicraft 175
2001 90 merc 2s

Just purchased..boat with a few elect issues it seems. When I first got the boat recently the first indicator, the starting battery needed charging but my smartchrger kept getting charge errors and until I disconnected all attached wires it then charged fully then I reconnected the wires and the next time I put the chrger on it seemed of with all wires on. The tach was very erratic from the start but yesterday I noticed the voltage gauge was bouncing from just under 13v to zero but only occasionally..it would be one or the other until I freaked and decided to take her to the trailer. It sounds like wiring issues but I'm braindead on 12v electric system but it seems the manual is saying the power to most gauges comes from ign switch but doesn't the tach get power from the stator on the motor? I guess I need some *basic troubleshooting tips.

Re: Erratic tach and voltage gauges..maybe others?

From this forum, this may help

Re: Erratic tach and voltage gauges..maybe others?

Thanks for the link, the local merc-man pointed to the throttle/ign control box..maybe a chafed wire and I guess it's fairly common since it's stuffed with wire. We'll see

Re: Erratic tach and voltage gauges..maybe others?

just an update...

Actually, it looks like it was the spade connections on the main wiring harness inside the engine, the merc-man says it was a known problem of mercs for 15 years and until the opti.. it was not changed.