I have a 2004 SD 187.
So today I was out on the boat messing around with my Garmin which is hard wired into an Acc. switch on my rocker panel when all of a sudden the Garmin shut off as did the light on the accessory rocker switch. The light on the Main Power switch stayed on. After flipping the other switches I discovered nothing would turn on (light on switch also did not turn on.) I then turned all switches off for a while. About 30 minutes later I turned on the main and the light came on, which I expected. I then flipped my acc. switch and it worked and my Garmin came on. I then turned on the stereo with no issues. After about 10 minutes or just listening to music while anchored, the same thing happened, everything turned off (no power) except for the Main switch. After swimming for about 20 to 30 minutes we got back on the boat to head home. Turned my switches on and everything worked all the way home, well the Garmin did since it was the only thing I had on, but I tested the other switches and they worked.
At first I thought maybe it was a breaker on the panel but none of them were popped out. It's almost as if there is too much draw and it is killing everything except the light for the main switch.
I am not very knowledgeable when it comes to the electrical system and am contemplating on bringing it to the dealer but I figured I would reach out for help here first since I am sure it will cost and arm and a leg to look at it.