Farm Equipment - Alternator Wiring on B

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Alternator Wiring on B

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=141130
Printed Date: 18 Jul 2025 at 11:51am
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Topic: Alternator Wiring on B

Posted By: George Davenport
Subject: Alternator Wiring on B
Date Posted: 05 Aug 2017 at 12:48pm

I have a Delco SI 10 3-wire alternator using a 12 Volt Ground Pos battery. The main electrical circuit consist of the ignition coil and starter. I am not sure where the black wire from the 2-wire plug attaches. I have the main battery (RED) wire attached to the Batt ery terminal and so is the red alternator wire from the 2-prong socket.

When I get the alternator functioning, I plan to attach a small sprayer motor into the circuit. Where will I wire my source? Thanks for your guidance.

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Life is what happens while you are making plans for the future

Replies:

Posted By: DougS
Date Posted: 05 Aug 2017 at 1:05pm

First, does your B have a magnito or does it have battery ignition? The two wire connector has one wire that goes to the BAT terminal, as you described. The other wire goes to the ignition circuit. If you have battery ignition, run this to the igniton side of the main switch, through a 47 ohm 1 watt resistor. You can also use a diode - with the polarity band facing the alternator. If you have a magnito you'll need to install a switch that goes to both the battery at one end and the alternator at the other end. A momentary push button switch will work, but you need to remember to push it after every engine start. I like the idea of using the 47 ohm resistor, even if not needed. It will limit current in case of a short. The large BAT terminal at the alternator goes to the ammeter, as it would have with the original generator. I presume you've changed the system from 6 volt positive ground to 12 volt negative ground. If not, you need to do this before attaching an alternator wire to anything.

Posted By: George Davenport
Date Posted: 05 Aug 2017 at 3:46pm

UPDATED INFORMATION: I am using a Ground Negative system. I am using a distributor , not a magneto. Please offer comments on this Updated situation. Thanks

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Life is what happens while you are making plans for the future

Posted By: Gerald J.
Date Posted: 05 Aug 2017 at 5:38pm

The resistor is needed in the alternator exciter wire when its connected to the ignition circuit. Without the resistor the alternator will back feed through that connection and supply ignition power so the ignition switch won't stop the engine. The diode does the same thing as does a dash lamp that can be an alternator failure light.

Gerald J.

Posted By: DougS
Date Posted: 05 Aug 2017 at 7:40pm

Wire the alternator excite wire to the ignition side of your ignition switch, through a diode, resistor or lamp. If you went fancy and installed a keyswitch with an accessory position, you can run the alternator excite wire to the acc terminal on the switch, no resistor, lamp or diode needed. As for your accessory motor, take it directly from the battery terminals. Fuse the + wire at a place close to the battery.