Starter engine dead after mixing battery terminals.

[Sigge]

Mercruiser inboard
model MCM 3.0 litre. Nov 2006
Family 6M9XM03.02VC

I made a stupid mistake when refitting my battery after winter.
I mixed the terminals plus/minus.

I realized my mistake when I got sparks trying to fit the plus terminal.
Fitted the terminals correct.

Now my starter engine is dead!?

I’ve found two curcuit breakers in the engine compartment. None of them were blown.
Any ideas what’s broken.

​​​​​​Maybe the starter solenoid or starter slave solenoid? Can I test them anyhow to see if they are broken?

 

[Bondo]

Ayuh,....... Welcome Aboard,..... Yer boat is new enough, it may have the square plastic fuse where the battery cable attaches to the starter,.....

 

[Sigge]

Thanks for the quick reply Bondo.

I think I’ve found the fuse? (see arrow at picture)

How can I see if It’s blown?

 

[Bondo]

Ayuh,..... That's it,..... With a test light, there should be power on both sides of it,.....

 

[Sigge]

I got a positive test light at the green arrow.... but not at the red one.

So I guess it’s the fuse that’s blown then?

Can I buy that fuse online?

 

[Scott Danforth]

all marinas would have that fuse in stock.

 

[Sigge]

I was thinking ..... maybe I could demount the fuse and bypass it just to see that that the fuse is the only problem and nothing more?

Just to test and see that the starter is working?

..,,,,or is that a bad idea?

 

[Bondo]

Ayuh,.... Go for it,.....

It was never there til a few years ago,.....

 

[Sigge]

Did bypass the fuse.... starter-rmotor working!!!

Thank You Bondo for support.

Now I’ll buy a fuse and mount it.

Confirm it should be a 90 Amp fuse?

 

[Bt Doctur]

The issue I have with that wiring is whaen the fuse does go bad from corrosion or just stops working is the complete boat system goes dead. Your main wiring is protected bty the 50A circuit breaker already . I have been reoving the Red wire and connecting it directly to the battery post and using a Maxi-Fuse type in place of the block . Size the fuse based on alt output usually 55 A and you r never going to be drawing that much .Ive used 40`s with no problems.
Wired this way you only lose the charging system but the motor will still run to get you home.

 

[alldodge]

Confirm it should be a 90 Amp fuse?

Yes, that was the original size