Upgrading the Alternator

[bayates]

I am upgrading the alternator on Hakuna Matata.  I bought the upgrade from Maine Sail and can't wait to get it installed.  But I am brain dead on the wiring.  I do not want to pull it apart as it works now and the normal rule is do not touch it if it is working.  As I look at the connections my mind looses it and I am not sure anymore what goes where.  I am looking to the experts here to help me understand what wires on the old 54A Mando unit go where on the new 74A unit.  I have attached the picture of each one so maybe someone can help me out. 

Thanks in advance.

[Stu Jackson]

Brian you're not the first with this quandry.

Here's how I did it:

Alternator Regulator Wiring Diagrams - all three http://c34.org/bbs/index.php/topic,4548.0.html

Draw some diagrams and it becomes a lot clearer.

Good luck.

[KWKloeber]

[edit]
**
note that the diagrams that Stu links to are correct for his and most OEM Motorola/Prestolite Alts [M-25/XP/35, etc) but the B series Alts and harnesses have a slightly different wiring setup.
••

I previously uploaded the schematics for the A and B series Engines on the TechWiki.
They are under the MANUALS topic.
There's a TON of info on the wiki all over.

The orientation of the alt in the schematic is correct (ie, up is up.)

You can tell what's what by:
- The orientation of the schematic.
- The number of wires on each terminal.
- The markings next to the Alt terminals.

Note that alt is not directly a drop-in.

Your field excite terminal is a post/nut and the new one a connector you butt crimp onto your snipped field excite (IMO not as good) but you can't do anything about it.). HOWEVER the new setup isn't a direct replacement because:

1)  The B Alts have two wires on the field excite terminal post (part of Westerbeke's convoluted wiring of the fuel pump/oil pressure switch). So you'll need to crimp the two current field excite wires to a step-down butt connector (adhesive heat shrink, use FTZ BRAND!!), then crimp to the pigtail on the new alt.  Or use an uninsulated step-down butt connector and cover w/ adhesive heat shrink tubing.   JUST my guess but I'd believe you'd need to use a 10-12 x 14-16 step-down butt connector.

2)  The B series alt has a SENSE terminal (a good thing) and the new one doesn't.  So there's another wire from the ALT OUT (B+) cable terminal (integral to the cable, not just on the Alt terminal post) that jumpers to your Alt SENSE terminal. The new alt doesn't have a SENSE (it's internally sensed) so you'd have a wire/terminal dangling free to corrode/contact something. You'd need to clip off the terminal and use a heat shrink WIRE END connector (essentially a heat-shrink-on wire nut) to close off the dangling sense wire.  Or you could close the wire end off other ways (there's several that could work - but it wouldn't be "proper" so to say.)

Lastly your Alt doesn't have a Neg cable to go onto the new Alt B- terminal.  A Neg cable should be added (IMO) while you're doing the switch.

51 to 74 is a modest jump to make (IMO) for all the hassle it causes if your current Alt has no issues.  Why do that - if you need more charging (for how you use the boat) why not make it worthwhile for the hassles?

Sorry for TMI, but it's not as simple as your question makes it out.  In short while that Alt could be "installed" it is a "drop in" for the M-25/XP but not for the B series engines (M-25XPB, 35B...)

Additionally I believe I read other posts where the Alt adjust arm needs to be changed or modified when putting it on the B engine.  I could be CRS about that issue/problem, so search the forum for those type messages/topic.  RC is aware of that Alt arm issue and could have suggestions.

[Stu Jackson]

Ken's right.  My diagrams are NOT for your old alternator, or your new one which seems to be internally regulated.

The PURPOSE of me showing you what I did was simply to get you to relax and get organized, by taking it step-by-step, wire by wire.  I had the same "overwhelmed" so I slowed down and drew it out, and it started to make sense.  That's why I posted my "homework" 'cuz you're about the 20th person who has asked.

In your case, it's actually simpler, because although your new alternator has a ground lug, it's basically the same other three wires that connected to your old one, WITH KEN'S IMPORTANT MODIFICATIONS.  You should BTW install a new ground from the alternator to the block rather than depending on the case and the bracket.