I have a 1999 Merc. Promax 300. Last year installed new powerhead and it runs great. Occasionally when I go to start the motor, I turn on the ignition switch and nothing happens. When I meen nothing,I mean no test buzzer, no fuel pump and even the trim stops working. If I go back to the motor and pull the fuse on the wiring harness and reinstall it the computer resets and I can operate the trim from the motor itself. Sometimes this solves the problem and the boat will act like normal. Some times I have to do it a few times to make it work. Any thoughts welcomed.
<br /><br />Start at the battery. Make sure the connections are shiny-clean and the fasteners are good and tight. If you have wingnuts, grab a pliers and reef on them.<br /><br />Another possibility is the connection at the main harness. Pull that apart and check for corrosion and pushed-back pins.<br /><br />It could also be a bad key switch, although that wouldn't affect the trim function.