Mercruiser Trim blows Ignition Fuse

[B.E. Anderson]

Hello Everyone,<br /><br />I am having a problem with my 120 HP Mercruiser I/0 blowing the 15A ignition fuse. I initially thought the problem was the temp. gage, but I was mistaken. (Glad I had extra fuses this time..)<br /><br />I believe I have narrowed it down to the upward trim, as I have now duplicated the problem twice. The fuse blows when I attempt to trim the motor up, but only under a heavy load. Both times I had just pulled a skier up with the trim all the way down. As soon as I tried to trim up, the main ignition fuse blew. With the motor running, but not in gear, I can trim up and down with no problem.<br /><br />I don't know which angle to look at this from. I fear that perhaps the trim pump motor is going bad and draws too much current under a load. I want to believe there's a simple short showing up somehow, but I can't imagine how that would only be manifested under the load condition. I haven't yet acquired any schematics yet, but I am really annoyed that this problem blows the main ignition fuse... Talking about "dead in the water"....<br /><br />Any thoughts or ideas would be greatly appreciated.<br /><br />Thanks,<br />Brian

 

[JB]

Re: Mercruiser Trim blows Ignition Fuse

Moving to I/Os

 

[B.E. Anderson]

Re: Mercruiser Trim blows Ignition Fuse

Whoops - Sorry, Didn't realize I was posting to the wrong place. Thanks for getting this where it belongs.<br /><br />Brian

 

[B.E. Anderson]

Re: Mercruiser Trim blows Ignition Fuse

Hope it doesn't make anyone mad, but I'm posting to myself to move this back up the list. I was afraid the inital chatter might have made you think I had gotten an answer already.<br /><br />Thanks,<br />Brian

 

[B.E. Anderson]

Re: Mercruiser Trim blows Ignition Fuse

Thought I'd give this one more shot. I'd sure appreciate some input.<br /><br />Thanks,<br />Brian

 

[TwoBallScrewBall]

Re: Mercruiser Trim blows Ignition Fuse

That fuse does not actually power the trim pump, it just activates the solenoid that powers it. The trim pump itself usually uses a 50A fuse or breaker. <br /><br />You might have a short somewhere in the harness that goes from the switch to the solenoids. Or the problem could be the solenoid. I don't think it's likely to be the pump itself so that's good news for you. <br /><br />I'm not sure off hand but I don't know why the trim switches would be wired through the main ignition circuit. Might be part of the problem, perhaps along the way somewhere it got piggybacked on to it and it shouldn't be, hence the overload. <br /><br />Good luck!

 

[Trent]

Re: Mercruiser Trim blows Ignition Fuse

Go back to the transom plate (inside the boat) Your wires for the trim limit and trim senders come thru here. These wires look like black lamp cord wire. Their connected with bullets connectors. Disconnect them and plug them into themselves. This bypasses the wires and sendors out in the outdrive. Now go and see if you can blow the fuse now. My bet is its fixed. These wires out in the outdrive rot and then short out. The one thats giving the problem is the trim limit, which is the port sending unit on the outdrive. Let us know if this fixes the problem.

 

[rattana]

Re: Mercruiser Trim blows Ignition Fuse

Brian if you have a multimeter, you can verify if you have a short in the wiring of the control circuit for the trim up solenoid. Just measure the resistance between the up signal wire on your solenoid and the engine block or negative battery post.

 

[rattana]

Re: Mercruiser Trim blows Ignition Fuse

I think Trent nailed the problem.

 

[B.E. Anderson]

Re: Mercruiser Trim blows Ignition Fuse

Thank you all very much for your replies. Trent, you NAILED it. Both sets of wires from the senders are extremely brittle. I first thought the ones from the limit sender must be so brittle because of high current, but not so. The wires from the other sender (which are not even connected on this boat) are just as brittle. I mean, you barely try to flex the wire and the insulation just disappears in a cloud of dust, and that's INSIDE the boat. The wires between the sender and the transom already had places without any insulation.<br /><br />So, now it makes perfect sense... With the boat still in the water, the routing (and stiffness) of the wires doesn't allow them to come near any metal, so trim up and down works fine. But, get the boat moving and some turbulance around the<br />wires so they can find a ground, trim up at the same time - pow....<br /><br />I haven't bypassed the limit sender and put the boat in the water to test the theory because it's obvious to me that this is indeed the problem. Were you suggesting that I bypass the limit sender just as a test and not as a solution? What are the ramifications of bypassing the limit sender and running that way? I don't think I can replace the wires without pulling the outdrive loose and I really don't want to tackle that right<br />now if I don't have to. I will though, if running<br />without the limit sender will cause any unsafe<br />conditions or potential damage to the boat.<br /><br />Again - THANKS so much. I hope this helps someone else.<br />Brian

 

[Trent]

Re: Mercruiser Trim blows Ignition Fuse

To put you at ease... The early outdrives did not have a trim limit or sender for that matter. Iv bypassed a bunch of them. Just dont raise the drive to high while the engine is running. You can actually do this from now on if you like. Fixing the problem is a PAIN in the rear for someone that's never done it. Id just fix the wires inside the boat and connect them to themselves and have fun. Glad you found the problem.

 

[tryan]

Re: Mercruiser Trim blows Ignition Fuse

i had to trim an inch off the trailer interlock wires. it's a simple repair with a phillips head and a small allen key.

 

[Tayler]

Re: Mercruiser Trim blows Ignition Fuse

I have a 3.0 Mercruiser on a 1996 192 RS Stingray. A couple of weeks ago we were out and every time I punched the throttle forward I noticed a small ?bog? or loss of power. The engine seemed to step up and run fine after the slight hesitation. A week later we were out and we got under way the same thing happened but the boat ran fine. We stopped for awhile and started it back up got going and then the engine lost electrical power. I snooped around and saw that the ignition fuse had blown. I rooted around and wiggled the wires @ the ignition fuse, replace the connection @ the battery terminal for the power supply to the GPS (totally independent from the ignition circuit) because I saw corrosion. I replaced the 10 amp ignition fuse and started her up again. Punched the throttle and the thing bogged and after about 100 feet the fuse popped again.

After a long tow home and vicious sunburn I got into the wiring and started to clean house.
-Replaced ignition switch ? Broken terminal
-Cleaned all grounds on engine block and @ battery ? corrosion
-Replaced fuse bus and ground block attached to the bus ? corrosion

The engine ran fine at idle in the driveway. I thought that I had the gremlin out of the boat. We got it out on the water and ran it for about 20 minutes WOT and got to the ramp picked up some passengers and 100 feet after we left the fuse popped again. After doing some research I have found a common issue with owners of boats with this motor and its ignition fuse popping. Nobody has seemed to find a particular cure or fix for this.

There are a lot of suggestions as to its cause.
The purple wire coming from the ignition switch having to much draw.
I.e. gauges, accessories or powering engine components.
The lead on the starter
The Alternator
Hydraulic trim pump
Blower
Throttle handle

Essentially anything that the purple wire goes to. I have checked all connections and they seem to be good. At this point I am at a loss. I disconnected the purple wire from the ignition switch that goes to the gauges to see if the short was there and the fuse blew again.

So logic would tell me that the short or issue is somewhere between the ignition switch, throttle handle or engine components. Any help will be greatly appreciated. The boat is at the shop and the guy has my radio pulled saying that that was the cause. The radio is not even connected to the ignition switch and the fuse blowing was happening before I installed the radio. It is on its own fuse on the bus. Seems to idle fine and only blows after the engine has run for awhile and at higher RPM?s. After that the fuse just keeps popping until you let is sit for awhile.

Thanks in advance Tayler

 

[Tayler]

Re: Mercruiser Trim blows Ignition Fuse

The shop placed a breaker off of the starter which keeps the fuse from popping. I read this post and it seems to make total sense now. I would rev up the engine and start to trim up on planing when the problem started happening. I hope you all don't mind me posting this here as I only want to help others with my point of view. The problem occurs under a load on the engine, I did not even think about the trim limit switch. I have bypassed the switch. (hope you meant connect the purple wire to the blue wires) I will test it today on the water and post back with results. I hope this fix works.

 

[Don S]

Re: Mercruiser Trim blows Ignition Fuse

Welcome to iboats.
Start a new thread for your question, don't just stick your question on the end of someone elses post. This one is 4 years old.