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Old 07-03-2024, 09:06 PM   #1
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Default Popping Ignition Fuse when Key Returns to On Position

Hey All, been spending some time reading the electrical section of the forum, as well as searching topics, yet haven't come across this issue yet.

Boat: A 2000 2100SR
Motor: 5.7 Mercruiser
Problem: Ignition Fuse

Backstory: I knew the starter was weak and was going to be replaced this year yet tried to start the boat anyhow after its initial uncovering. A battery terminal started to smoke and melted the negative terminal on one battery.

I fixed the wiring damage, replaced starter, replaced both batteries, cleaned all remaining terminals and had no power; however, I learned the ignition fuse was popped. Yay, problem found. Nope.

Every time the fuse was replaced the boat would crank until the ignition was allowed back to the on position were the fuse would pop again.

Then the coil was replaced, ignition key replaced, checked main engine ground (appeared to be in good condition), checked power at the 50amp fuse, and the alternator was bypassed to see if it was causing the fuse to blow.

But same problem persisted when the key went back to the on position.

Buddy and I are at a loss where to search next for possible short/power surge. Any insight or recommendations are highly appreciated. Thanks.
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- 2000, Maxum 2100 SR 5.7 MerCruiser
- 1985, 15ft Zodiac Pro 60hp 2-Stroke Mercury
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Old 07-03-2024, 11:56 PM   #2
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Welcome aboard!

Let’s try to isolate the issue between the cranking circuit and ignition circuit. Try Turing off the kill switch on the shifter which will remove power from the ignition circuit. Does the fuse still blow when cranking the engine over? If yes it’s an issue with the starting circuit if no it’s an issue with the ignition circuit.

Under Documents of this site you will find the Mercruiser manual for you engine which includes the engine wiring diagram. Let me know if you or your buddy are familiar with reading wiring diagrams and if not I can help you through the next steps.

Also is this a carburetor or fuel injection engine?
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Old 07-04-2024, 12:08 AM   #3
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Thanks for response, Captain. Yes, we're familiar with reading diagrams and will download the manual. We'll also try the recommendation of turning off the kill switch and see if there a "yes" "no" based on the recommendation.
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Old 07-04-2024, 12:10 AM   #4
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Quote:
Originally Posted by TobyB View Post
Thanks for response, Captain. Yes, we're familiar with reading diagrams and will download the manual. We'll also try the recommendation of turning off the kill switch and see if there a "yes" "no" based on the recommendation.
Great! Let us know how you make out and if you have any questions.
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Old 07-08-2024, 06:49 PM   #5
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Hey Captain Mike,

We went through the kill switch and it was working correctly then were able to isolate the problem to the engine side. With no real answer, the boat stopped blowing ignition fuses and would start and run for 5 - 30s before shutting off.

We continued testing was in order with the next being the oil pressure switch, oil pressure sending unit, and fuel pump which all checked out fine.

We then went back the new starter and the starter appears to have an internal short. The meter was showing short when going from the yellow/purple wire connection to the side of the starter (believe that is what my mechanic was saying as I wasn't down there).

Unless, there are other ideas. I will likely pull the starter tonight and see if anywhere can test it as the boat shop can't from what they said this morning.
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Old 07-08-2024, 09:02 PM   #6
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Hi Toby, sounds more like the short is in the starter solenoid but it should have come with the new starter. Most auto places should be able to test it. Any idea if you can return it?
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Old 07-10-2024, 07:21 PM   #7
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Quote:
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Hi Toby, sounds more like the short is in the starter solenoid but it should have come with the new starter. Most auto places should be able to test it. Any idea if you can return it?
Hey Captain,

Yes, the short was in the solenoid and the boat shop said they don't test starters yet they replaced it.

Installed new new starter last night and boat fires up, purrs like a kitten, turns off, doesn't blow fuses, and operates like normal.

I'll stick around the forums and try not to be a one-stop user. Thanks for all your help @mmwjr.
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Old 07-10-2024, 09:46 PM   #8
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Toby that’s great news. Yes feel free to stick around and post you knowledge as well as asking questions.
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Old 07-11-2024, 07:15 PM   #9
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Get to go crabbing Saturday now and will do. Have a great weekend, Mike.
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