Stumped, need a place to start troubleshooting

Dutch320

So I was at my boat last night and fired up the motors and everything worked perfectly, let them warm up no problems. Fast forward to today and the port engine works as it should but starboard just cranks and the tach jumps around. Last night I was checking the navigation lights after running the engines and if I switched to navigation on the switch it would turn some of my gauges on (fuel and oil pressure and one trim gauge) also moves my trim tabs and sets off the warning horn on the Lenco box inside the dashboard. Haven’t done anything new that might have caused this and the navigation lights worked fine last week. This is on a 2007 320 with twin 5.0 liter. Any ideas would be great. 

LaRea

Maybe a ground issue?  Find the ground block (probably in the engine room) and check the integrity of every wire attached to it.  

That wouldn't explain the engine, but it might explain the other weirdness.  

212rowboat

do same this @LaRea mentioned, but behind dash panel.  sounds like the work of corrosion- not as predominate in fresh water as salt, but it's still a boat and they still float atop water.  

a chunk of patina is conductive.  a broken wire on your switch or on your safety kill switch will cause this as well.... if i were to say which is more likely, it's a combo- wires becoming fragile because of corrosion, and a good bounce and it breaks... 

Dutch320

Thanks, I’ll be at the boat in the morning checking what you have suggested. 

Dutch320

Just wanted to give an update in case anyone else runs into the same issues. Although both problems presented themselves at the same time @LaRea was correct that they were unrelated. Turns out the motor issue was solved by replacing the cap and rotor (did the other one too), got lucky first thing I tried lol. The other issue of the nav/anchor switch reeking havoc with my gauges and trim tabs appears to be a bad dimmer. Not sure who posted the wiring diagram for a 342, but you saved my a$$, thank you!  Unplugged the dimmer and everything works as it should. As of now it’s seems as though all is good. Below is the cause of the problem.

Handymans342

Good catch

Dutch320

Thanks @Handymans342, I thought today was gonna be filled with banging my head against the wall and drinking to much, so far no banging my head. 

Aqua_Aura

That dimmer seems to cause bigger issues than I would think it is capable of. I don't think this is the first post about switch issues and the dimmer being the cause