Re: switch problem '86 190V
Try looking at your fuses, and your fuseblock.
Even if the fuses are OK, it's an old boat and corrosion can make for a weak or bad connection between the fuses and the fuseblock sockets.
This has happenned to me several times on my '89 224; something doesn't work, I take the fuse out, it's OK but replace it, or clean it with emery cloth, also clean the fuseholder, put the fuse back, and then it will work OK.
I am so frustrated that I will be replacing the boat's fuseblock with a new one to eliminate future problems. Switches seem to be doing well, I have had no issues with any of them.
For troubleshooting, you can use a voltmeter: Turn the item on, measure the voltage on the fuse socket (not the fuse, but the socket) on one end of the fuse to the device, then measure the voltage on the socket to the other end of the fuse; if both voltages are the same, problem is elsewhere, if voltage is different, current is not making its way across the fuseblock to the device and you can try the cleaning.
Hope this helps.
Jorge