2007 Mercury 90hp 4-stroke EFI Alternator not charging 84-878231T05 fuse blown

[Dan Mangan]

I wanted to share with everyone what I learned about alternator not charging on my 2007 Mercury 90hp 4-stroke EFI. There is a cable (part number 84-878231T05) that goes from the alternator to a common 12V post. On that post there is 3 other cables. 1 comes from battery 2 is the starter cable 3 is a jumper to a solenoid and the 4th is the cable from alternator. The alternator one has a 100 amp fuse incased in some kind of sealant glue and the fuse is non-ser viceable. I noticed with the engine at idle i had 22-24VDC at the post on the alternator but only 11VDC on the common post (other end of that cable) I disconnected all 4 cable at the common post and did not have continuity through alternator cable because that 100 amp fuse was blown. I called my dealer and he said yeah those blow all the time if the battery cables ever touch or polarity is reversed even for a split second. I called a local alternator repair shop and told him the story and he said that 22-24VDC is normal because of the blow fuse, once the fuse is good that voltage will drop to 13-14VDC.

A new cable is $90!!! I came up with the following solution instead of buying that cable. Hope this helps someone in the future. I went to a car auto place and got a 100 amp inline fuse holder and spare fuses for $20

 

[Risland]

I've learned to use the internet to search out answers, this one really paid off, THANK YOU VERY MUCH! Had similar problem with my 2013 115 Merc 4 stroke EFI, ran real rough all of a sudden, thought might be fuel, fuel lines. Wound up adding a great item, Mercury Vesselview Mobile to my engine, gave me a fault code about the electrical. Traced it down and found the same thing as you had a blown inline fuse. Like you, instead of buying the over priced new cable with fuse, I added an inline 100 amp Maxi fuse holder and fuse. BINGO! Now putting out 14.25 amps at idle to start battery. Just no real idea why this happened, but with this fuse holder easy to replace fuse if needed. My addition was less than $20.
Thanks again for your post.

 

[GA_Boater]

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