Alternator wiring

Rus Jones

Rus Jones

.
Nov 23, 2017
6
Hunter 30 Biloxi Mississippi
I'm hoping someone can help me here. My current alternator doesn't seem to be charging. My 78 Hunter 30 had a new or perhaps rebuilt alternator still sealed in a vacuum wrap. Everything about the alternator looks the same, but the two pin plug is different than the older alternator. I'm trying to figure out which of the two terminals is #1 and which one is #2. From what I've read #1 will go to the idiot light, and #2 will tie into the hot wire from the battery, but I need to know which is which. I have a 50 percent chance of getting it right, but I would rather know that I'm right. There are no markings on the alternator to tell me which is which. I'm attaching a photo.
IMG_5895.JPG
 
D

dlochner

.
Jan 11, 2014
12,435
Sabre 362 113 Fair Haven, NY
Rus,
A couple of suggestions. For the alternator that is not charging, take it to an alternator repair shop. These are a basically automotive alternators, so any competent shop should be able to help. The usual culprit is blown diodes because someone changed the battery switch while the engine was running.

Follow the wires. If it is not clear use a Digital Voltmeter in the continuity mode to check the circuit.
 
Rus Jones

Rus Jones

.
Nov 23, 2017
6
Hunter 30 Biloxi Mississippi
Thanks for the info I appreciate it. I'm still wanting to go ahead and change the alternators out since I have this new one, and I'll have the other rebuilt as a back up.
 
capta

capta

.
Jun 4, 2009
4,889
Pearson 530 Admiralty Bay, Bequia SVG
From what I can see the terminal are very clearly marked E and BAT. The plug should be the control circuit.
There are references online that show almost every alternator and it's hook up. You don't even need to know which alternator it is, because they are pictures of the alternator backs.
Here is one;
alt book.PNG
 
Maine Sail

Maine Sail

.
Feb 6, 1998
11,697
Canadian Sailcraft 36T Casco Bay, ME
That looks like an aftermarket / Chinese Hitachi unit, some are OK and some are pretty poor. Hard to tell without a model #..

If so the cross of the T is "R" or +12V/sense and the vertical of the T is "L" or dash lamp. These units are also isolated ground and will not work without connecting the battery bank to one of the B- terminals.
 
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