1984 Mercruiser 265 (5.0 L V8, GM)

deputyb

Cadet
Joined
Oct 27, 2009
Messages
7
I have googled the snot out of this and can't locate an answer. I have the above engine in an 84 Cruisers Inc 22' Barnegat. It quit charging the batteries. (new this year) So I replaced the alternator with a one wire unit and still shows no voltage at alt. post. wire from this post runs to a box (coil? transformer?) marked Battery (wire to battery now jumped to here) and the other big connector says Alt. a ground wire a back of this box is grounded. what is this box? other than possibly a bad alternator (new from NAPA), why isn't the battery charging. 10V shows pretty steady on dashboard volt meter. fishfinder says 8.4 to 10.8 volts. thanks guys.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,476
One wire alternators should not be used in boats

Your alternator is either not sensing battery voltage, or the alternator isnt working.

Make sure every wire connection from the battery to the block to the alternator is clean and shiney
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,701
Post a pic of the box, its probably an isolator and the diode inside has burned out
 
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