Crossed battery terminals 4.3L Mercruiser Alpha1 out drive Gen 2

[BopsBuddy]

I've seen this topic elsewhere, but have specific questions. I crossed battery terminals and smoked my alternator. I've read it needs to be replaced. Check. I've read there is a fuse to replace, but do not know specifically where it's located. The boat turns over, but won't start. Thunderbolt IV ignition system. I've never had a hard time starting this motor. I'm not a mechanic so testing/jumping stuff isn't an option. What else should I consider replacing? Any help is appreciated.

 

[Scott Danforth]

I would suggest you learn how to diagnose simple systems. Harbor freight has digital volt meters that are free with a coupon or about $8 normally

Or you can replace everything - battery, cables, circuit breaker, ignition, etc.

Personally, i would diagnose what you fried, and only replace that

 

[alldodge]

Howdy

Agree it would be best to test and find out what needs replacing.
There is a 90 AMP fuse which is mounted on top the starter lug where the battery cable is connected. It looks like the pic in link below and can be found here at iboats. The fuse is there to protect the system if the alternator shorts out, as yours did

http://www.iboats.com/Mercruiser-Fuse-Kit/dm/cart_id.344045398--session_id.113466785--view_id.270259

 

[Bt Doctur]

The fact that it is cranking may be a sign the 90A link if used on your boat is still good. Check under the dash for a 20A inline fuse on the purple wire.
Downside is you may have blown the electronic module

 

[BopsBuddy]

Thank you alldodge and bt doctur. I just needed to know where the fuse is and the diagram helps. I think electronic module is blown.

 

[Bt Doctur]

Dont, Think, TEST IT You need 12v at the positive side of the coil for anything to happen , check there first.

 

[gm280]

There are so many circuits these days to keep reversed polarity from frying everything that is seems amazing that you don't see more available for situation like boats and such. It use to be they used a directional diode to solve that. But that allowed a pretty substantial voltage drop across that diode, and that want good. But now with high power MOSFETS their no time resistance is the micro-ohms scale and can easily handle hundreds of amps. It would surely prevent this from happening. JMHO

 

[Scott Danforth]

Darwinism sells parts

 

[Bt Doctur]

After you verify 12v at the coil, if you want ,remove the module and mail it Priority Mail Flat rate, think its under $7.00 and I will bench test it to confirm the diagnosis.
Unsure about the electronics in the dist module but you could have only damaged it and thats why you lost spark.

 

[BopsBuddy]

Awesome. Thank you for the advice. Working on it now...

 

[BopsBuddy]

Update....my motto does NOT have the 90 Amp fuse. All of a sudden I had spark! So, this complicated things as the motor would run perfect then die 5 mins later withnospark again. Took a hard look at the coil. Noticed it had a crack on top. Replaced it. It appeared to be original. Boat fired again and ran perfect again for about ten mins. I shifted forward and reverse to test gears since exhaust bellows and gimble bearing were replaced last fall AFTER I had winterized it. Shifting to reverse kills motor every time. Solved one problem to uncover another. I suspect the lower throttle cable was re-installed improperly causing something to kill the motor. I'm taking it to a different mechanic as the last clearly didn't do me any favors. I thought I'd update regarding the coil for others in my situation. I may still have ignition module issue, but unsure how to test other than replace. Either way, it's off to the shop now. Just trying to get it running properly to sell!