Mike, is that how yours is set up? I had an old I/O from the 1970's that was set up that way that
Greg is talking about, but I was just wondering how they set up the new dash light systems nowadays since I'm still waiting to put my hands on my new FW. I remember always wishing there was a way to control it on that boat without turning off the key.
BTW,
Greg I found your pictures on the forum after my previous post, so I did get to see your setup and that did help. Not sure my theory is valid-I'm no electrical genius. Wondering how the helm instrument lights could be coming on when the key is on and not blow the fuse, but at the same time the fuse blows when you flip that switch (if they actually ARE controlled by that switch you're asking about). I would think if you had some type of short in those lights themselves, then whatever fuse protects those lights would blow every time you turned the key. THAT is what leads me to believe that something is tapped into the circuit which is controlled by that switch-and it is overloading the circuit.
I don't think you said it earlier- do you know which circuit belongs to the fuse that keeps blowing? Is there a label in the panel telling you that? Maybe that would help you out? For example, I once had a car that the power windows would just stop working on everyone once in awhile because a fuse would blow-but it didn't have a label for "power windows." Instead, I had to figure out what else wasn't working when the windows quit working and I eventually found out that the power windows were part of the "power seat" circuit as it was labelled on my panel. Finally figured out after a year that my power lumbar switch was bad, and the fuse would blow only when "inflating" the lumbar support but would not if I was "deflating" it. I never fixed it, I just made sure the windows were up if my back got tired, so that the windows would be up when the fuse blew and I wouldn't have to be in a rush to replace it!
Finally, I guess there is always the possibility that there is something being controlled by the switch, but the switch itself has a short in it that is blowing the fuse only when switching it in that direction.
Mike is right, though, in his previous statement that electrical problems are very frustrating.

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Paul
2007 Four Winns Horizon 220Mercruiser 350 Mag MPI w/ Bravo III Drive
2004 Ford Explorer Limited (V8-AWD)
Pomme de Terre Lake (Southwest Missouri)