Mercruiser 350 Keep blowing 90amp Fuse while attempting to start

[fishngolf]

I was having issues with a sporadic idle and what I thought was a dead battery. I went and cleaned all the grounds in the electrical system and now when I go to start the engine the 90 amp fuse on the starter blows. No power at the gauges and no action on the ignition. I'm thinking its the starter itself as when I was cleaning contacts I noticed one of the terminals on the starter solenoid was loose. I want to test to make sure its the starter not the alternator or another short. I have a multi meter and want to check resistance. Can I try starting engine with the alternator disconnected? Can I hook up the harness connection which was on the fuse to a separate battery so I can test the starter itself?

 

[Bt Doctur]

Well something is wrong because the 50A circuit breaker protects the main wiring and the 90A link protects the alt output to the battery.The 90A is always hot so it would blow immediatly when the battery switch was turned on. If the Orange alt output and the Red system power wire are connected together disconnect the alt wires at the alt and report test results

 

[Bt Doctur]

The alt sense is a 16 Ga so it would be melted, only other point is the Yellow/Red going to the starter. If that was grounded or if the starters main solenoid was grounding it out
click to enlarge

 

[Bt Doctur]

deletes not working
The alt sense is a 16 Ga so it would be melted, only other point is the Yellow/Red going to the starter. If that was grounded or if the starters main solenoid was grounding it out
click to enlarge

 

[Blizzmet06]

This is the same setup I have.

 

[scoflaw]

This is the same setup I have.

That's a red wire not r/p and your 90 amp fuse is blown

 

[Blizzmet06]

That’s an image I found when researching my issue. Fuse blows every time I go to start. Don’t want to buy another just to blow again. Trying to find testing procedure with multimeter for battery cables, starter, and solenoid.

 

[Bt Doctur]

Remove the fuse and remove the Red and Orange wires from it, Cut the Red and Orange if necessary.
Using a jumper off the + battery touch the orange, should see no spark. Touch the Red , should see no spark
Remove the Yellow/Red large wire from the slave .Have someone hold the key on start, touch the Red wire. Solenoid should operate, You should NOT see and sparks or heavy current draw here.,
Touch jumper to Yellow/Red at slave. should see a small spark when solenoid opoerates and spins the motor
A large spark is a shorted solenoid

 

[fishngolf]

So I removed the orange alternator cable at the fuse and also disconnected everything at the alternator. I did notice the positive battery cable to the starter had poor insulation and looked to be in contact with the starter body itself. Could maybe have been my short. I hooked the battery up and it started no problem with the alternator disconnected. Any ways to test the alternator? I tired taking to automotive store but they couldn't bench test it.

 

[NHGuy]

Yes you can take the alternator to a parts store to test it. You must have found one that doesn't test. Replace it if bad or reuse it if good.
Then reinstall everything making sure the positive cable is properly insulated.

The LAST thing to do is attach the negative cable.

But you never start an engine with the alternator disconnected.
You may have compounded the problem.

Come back and tell us if it runs.

If it fails and Boat doc gives you advice, follow it exactly or we will be down this road again.

I'm sorry to be harsh, but some things need to be made obvious if they were missed the first time.

 

[Blizzmet06]

Found the main battery cable to starter had bad insulation and was shorting to the starter itself. Found that the IAC slots were stripped and replaced that. Boat idles better but still not 100%. Before I couldn’t keep it running now it will fluctuate between 590-650. Also think there’s some electrical issues as the cannon plugin moved slightly would kill the radio. Put a clamp on it to hopefully get better connections. Took it on the lake for a test run and noticed the automatic blower would intermittently turn off. Not sure if that’s supposed to happen or if it’s further proof of electrical issue. Boat ran fine between 1000 rpm and 3200. Would not go over 3200 even with throttle pushed all the forward. Stalled when I went to reverse in gear when loading back on trailer. I think IAc is still an issue. Mechanic said was only getting 2 of 4 signals and from what I’ve read the IAc needs both phases to work 100%. Not sure where to go from here. Mechanic said he can’t get his scanner to work on the mefi1 even though it says 93 and newer.