What Neil said and check the plug. The A-4 came from the factory with a "plug in harness" to connect to the ignition/gage panel. We here call it the "trailer plug". It is a plug just like the lights plug on a trailer for your car and it is notorious for causing problems as it is not sealed and corrodes with time. It can cause all kinds of intermittent problems. If you find a voltage drop the plug should be checked. Many of us have eliminated it or re-wired the engine circuits.
Most electrical issues can be traced to bad grounds on boats so start there.
Dave Neptune
