Freaking fuse redux

nipper · #1 07-24-2011, 01:27 PM

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?

THEFERMANATOR · #2 07-24-2011, 02:09 PM

DO NOT GO PUTTING IN BIGGER FUSES! This is a last resort for emergencies only, and most of the time results in melted wires or fires. You need to find out where the excess current draw is by finding out what all is powered off of that circuit. It could be a bad guage or a simple chafed wire somewhere in the harness, but putting in bigger fuses could cost you your whole boat if your not careful. Fires on boats is dangerous business and not something to be taken lightly.

step up here · #3 07-24-2011, 05:08 PM

sounds like a chafed wire some where and is only making a dead short when being contacted. possible some steering linkage or something moving that is grounded.when a fuse blows its always for a reason. really this should not be that hard to fine. follow the wire system at the fuse like ferm said. good luck

Destroyer · #4 07-24-2011, 05:09 PM

Quote:

Originally Posted by THEFERMANATOR

DO NOT GO PUTTING IN BIGGER FUSES! This is a last resort for emergencies only, and most of the time results in melted wires or fires. You need to find out where the excess current draw is by finding out what all is powered off of that circuit. It could be a bad guage or a simple chafed wire somewhere in the harness, but putting in bigger fuses could cost you your whole boat if your not careful. Fires on boats is dangerous business and not something to be taken lightly.

DAMN FERM... Now you're starting to sound like me...

Safety, safety safety.. it pays off big time guys!!!

Nipper, fuses blow when there is an excess current draw flowing through them. So you need to start with the wire(s) leading to that fuse and trace it/them forwards and backwards to wherever they terminate. Your problem will be in those wires or the units they terminate to.

THEFERMANATOR · #5 07-24-2011, 07:45 PM

Quote:

Originally Posted by Destroyer

DAMN FERM... Now you're starting to sound like me...

Safety, safety safety.. it pays off big time guys!!!

Nipper, fuses blow when there is an excess current draw flowing through them. So you need to start with the wire(s) leading to that fuse and trace it/them forwards and backwards to wherever they terminate. Your problem will be in those wires or the units they terminate to.

When it comes to fire hazards in a boat, I'm a bit paranoid. 6 years ago I was 40 miles out from Montauk when a 43 footer we were farrying from Boston to Englewood Fl caught fire because the tops of the tanks leaked and we had just filled em to the brim in Montauk. Close to 50 gallons of diesel splashing around in the rear bildge where the generator was running splashed up into the armerture of the 8KW Westerbeke and we had smoke pouring out. Fortunately the engines running sucked enough air through them that they kept it from getting nasty since it couldn't get any air. We got it put out and finished the trip, but I'm still paranoid about electrical issues on boats from that incident.

nipper · #6 07-24-2011, 08:18 PM

Thanks, guys. I was VERY reluctant to put in bigger fuses (even the 25A and then 30A fuses at the dock the MECHANIC gave me at the dock). That's why, after the 25A blew, I put the 30A in only in an attempt to get back to the dock, to no avail. My neighbor, who was in the boat with me at the time, has been urging me to just up the amperage a bit and go with 30A fuses in the panel and the wiring harness. NOT a good idea. Even with my limited knowledge, I know that wires are only rated for a given amount of current for a reason, and that is why there is a fuse to limit the amount of current to that which the wire can handle. Given that I suspect the short is in one of the 5 wires leading to/from the ignition switch, I will begin with those and go from there.

Thanks again for your help.

spareparts · #7 07-24-2011, 10:17 PM

may be easier to rewire than to try and fine the culprit. Separate the house electricity from the engine side, pull the engine harness out and lay it on the ground where you can really see it. Look for any signs of shorts. Run a main hot wire and ground to the dash for accessories and wire from there

Destroyer · #8 07-25-2011, 12:19 AM

Quote:

Originally Posted by THEFERMANATOR

When it comes to fire hazards in a boat, I'm a bit paranoid. 6 years ago I was 40 miles out from Montauk when a 43 footer we were farrying from Boston to Englewood Fl caught fire because the tops of the tanks leaked and we had just filled em to the brim in Montauk. Close to 50 gallons of diesel splashing around in the rear bildge where the generator was running splashed up into the armerture of the 8KW Westerbeke and we had smoke pouring out. Fortunately the engines running sucked enough air through them that they kept it from getting nasty since it couldn't get any air. We got it put out and finished the trip, but I'm still paranoid about electrical issues on boats from that incident.

Glad you made it ok. Lucky the engines kept the fire down. I completely understand. My brother almost lost his life in a house fire in Maine. He and his wife survived.. the other couple that were with them did not. I had to go get them and bring them home from the hospital...saw the results of the fire. House completely gone. Been paranoid of fire ever since.