Electrical ground
 

I having some what I believe to be ground issues with my 245. Most noticible is the tach jumping around everywhere. You push the horn the tach will jump to 4500. This does not happen when it is running. I have the service manual but the wiring diagrams are not specific to the locations of the grounds.

So from what I can tell. There is a ground block under the dash on the port side beside the ignition switch? But I cannot figure where it gets grounded from there. I'm guessing back on the engine block somewhere?

It also appears that the hot to the instruments has an issue. The wire from the ignition switch that goes up to the gauges gets very hot when the key is turned on. Almost like a short but not enough to trip a breaker.

I'd like to rip it all out and start over but I'm not about to start doing that in the peak of boating season. Any ideas?

Check the main engine harness plug on the engine for corrosion or a loose connection......

Yes I agree. I had the same problem a few years ago on my Scorpion 210 and it was green-rot in the rubber plug that was near the engine. Mine however would not even start as it was a complete dead key? I guess the manifold heat caused corrosion inside the rubber plug and it was not detectable until you unplugged it and looked inside. A little cleaning and electrical contact grease and I was good to go! No problems anymore.