Turn the running lights on and volt meter drops to 12V and engine will not accelerate/plane to save its life. Turn lights off throttle back and will accelerate fine. Lights work, alt is charging fine even when meter is readng 12V. Same thing happens with the blower! Do I have a couple bad connections shorting the ignition causing the misfire/breakup of the engine? I cleaned all the battery connections, grounds and dash switches and breakers. I also have a guest dual battery smart switch.

i had a friend last week his boat was running like crap,tach was bouncing all over the place... i found that the + cable going to the starter was loose,cleaned all the connections at the starter and the boat ran like a champ with no more issues..its amazing what a loose connection will cause..