2GM20 Alternator and Starter Wiring

jssailem · Jun 21, 2019

Welcome @APWTryfan

Andy. Your questions and more are answered in the articles on MaineSail’s site.
https://marinehowto.com/

A search of our forum will yield many threads regarding batteries, alternators, etc. one of our members @Stu Jackson has posted many responses to your general questions. Look for his Electrical 101 links to all you want to know plus some.

We look for pictures of your new boat.

Whatfiero1 · Jun 21, 2019

Most people disconnect altanator output and tape off then run a new larger gauge directly from post to selector switch

LeslieTroyer · Jun 21, 2019

You can move the alt out from common to 1 or 2 which ever is you house. Then read 1,2 or both thread under mussing with Maine sail. That will tell you how to wire the start battery.

Les

Stu Jackson · Jun 21, 2019

These are from my Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

If you have TWO SEPARATE WIRES from the C post of the 1-2-B switch to the starter and the alternator, yes, you can do what Les suggests. It's the other end of the same wire as if wiring to the house bank, but it would be better to run directly to the house bank from the AO and don't forget to fuse it at the battery end.
OEM 1-2-B Switch Wiring History http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
http://forums.sailboatowners.com/in...dc-electrical-foundation.181929/#post-1332240

The Short Version of the 1-2-B Switch Stuff: http://c34.org/bbs/index.php/topic,5977.msg38552.html#msg38552 This is a link to the Electrical Systems 101 Topic, reply #2

What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
http://forums.catalina.sailboatowners.com/showthread.php?p=742417 and http://c34.org/bbs/index.php/topic,9404.msg70131.html#msg70131

Making Sense of Automatic Charging Relays (2019)
https://marinehowto.com/automatic-charging-relays/

You should also be aware of this, especially with AGMS, which may not be your best choice.
Hitachi Alternators 101 http://forums.catalina.sailboatowners.com/showthread.php?t=166123 This comes up so often on other boating forums...

Good luck.

2GM20 Alternator and Starter Wiring

APWTryfan

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jssailem

SBO Weather and Forecasting Forum Jim & John

Whatfiero1

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LeslieTroyer

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Stu Jackson

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APWTryfan

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