Freaking fuse redux

[nipper]

I related in a couple previous threads my electrical problems with my 1991 V20 cuddy with 2006 Mercruiser 4.3 liter I/O. Problem began about 3 weeks ago when I suddenly lost all power except tilt and trim. No blower/bilge/navigation lights/fishbox, etc., and of course, no ignition and no power to instrument panel. 50A circuit breaker was fine. I replaced 90A fuse on starter solenoid because I had trouble with that (with exact same symptoms) last year. Turns out I did not need to do that because 90A fuse was fine. All fuses in the panel were fine as well. I took it to my mechanic who found a 20A blade type fuse in one of the wiring harnesses had blown. Mechanic said he checked grounds, confirmed they were good, but did not otherwise diagnose the source of the blown fuse.

So, I took it out Friday. I backed it off the trailer and immediately lost all power. I had a spare 20A fuse, so I put that in, and it blew again. I tied up to the dock, and it just so happened that the guy who owns the shop I took it to was there doing on water service to another boat. He had some spare fuses, but only 25A and 30A. We tried the 25A, did not lose power, pulled away from the dock and it died again. So, I stuck the 30A in, went another 20 yards and again lost power. So, I paddled Nipper/pulled her with a line back to the dock and called it a day. The owner/mechanic was gone by this time but I saw him driving by on my way home, flagged him down and he said to take it to his shop. I did, and while in the parking lot, out of habit, flicked the accessory switches to make sure none was on (even though no power--to the ignition switch or the instrument panel--duh) and found that I DID have power to the accessories, but not to the ignition or instrument panel. This immediately told me the 20A starter fuse in the fuse panel might be bad, and sure enough, it was. The 30A fuse I had put in the wiring harness was good. So, I stuck in a spare 20A fuse in the starter slot of the panel, and voila, I had ignition and power to the instrument panel. Kind of ticked off, and knowing the shop could not look at it until next week, I brought it home.

Today, I fired it up, all was well, ran it on the muffs for about 20 minutes, varying the throttle, putting it into and out of gear, shutting down and restarting, so I thought, hey, this seems good, so I shut it all down. I came back about 1/2 hour later, it fired up nicely, ran in idle for about 20 seconds and it shut down. The 20A fuse in the panel had blown again, leaving me with accessory power but no power to the ignition or the instrument panel. I replaced it with another (I have a bunch--see below) and repeated what I had done previously with running it for a good 15 minutes, starting it, varying throttle, shutting down, restarting, and so far so good.

My Dad bought this V20 new in 1991 and since probably the 2nd or 3rd year of service it would blow the 20A starter fuse in the fuse panel perhaps once or twice a season, some seasons not at all. Sometimes, it would blow 2 or 3 per episode then be fine. That's why he (and now I) always had plenty of spare 20A glass type fuses on hand. I do not know if he every tried to have the issue diagnosed--he probably did because he used a very good and conscientious mechanic. I have had Nipper since 2004, and I can only recall one episode of blowing the 20A starter fuse in the fuse panel.

So, it appears to my not electrical system inclined brain that there is a short somewhere, it has probably been there since boat was new/almost new given that the problem existed prior to re-powering with the new 4.3 litre in 2006, and it might be related to the ignition switch given that the re-power was with a brand new motor, including starter, etc.

Sorry for the long thread, but it is raining here, I am bored, and wanted to give as good a description of my frustrating problem as I can. So, I guess, my questions are as follows:

1. Any thoughts on what to do next.
2. Is there any easy way to check the operation of the ignition switch.
3. Is there any easy way to get to the ignition switch short of pulling off the entire panel which encloses the steering wheel? I can barely reach the ignition switch from the backside when I remove the fuse panel and the instrument panel, and do not think I can get it out that way.
4. How dangerous is it to experiment with putting a 25 or 30A fuse in the starter slot in the fuse panel and/or the wiring harness?