My bud has got a 97 checkmate that has a mysterious electrical problem. When he starts it up the voltmeter jumps back and forth and then settles down. It seems to idle fine but when you get on plane under load it starts missing and the voltmeter starts jumping again. We've checked the batteries, replaced the altenator(also disconnected it) checked the battery switch,cable ends and replaced the cap and rotor. We also ran it on a known good battery bypassing the switch and it still does it. Any suggestions? Could the gauge be causing this? We're stumped! Thanks for any replies.

I had an identical situation on my boat. Turns out the ignition wire is breaker protected and the connection from the switch to the breaker to the wiring harness was crap.

Only way I found out was an on plane misfire. I got pissed, kicked the panel in front of the drivers seat and the radio also quit

I have since rewired the entire dash...For every one connection in the engine compartment there are 2-3 under the dash...

Thanks. He did replace the switch last year, maybe something is loose or corroded.

look at main engine harness plug, seen some weird problems when it gets corrosion in there