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Old 03-02-2009, 11:21 AM
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GM 3 wire alternator idiot light hook up

I understand how to wire up the 3 wire alternator.



The number 1 wire goes to a resistor or dash light and is suppose to glow when not charging. That wire goes to a dash light. The Dash light has 2 terminals one for neg and one for positive.

This is my question: Is the wire coming off the alternator + or - ? When I plug it into the light I need to know if the other connector goes to ground or hot (pos.),.

Thanx in advance as always,

-=Fred=-

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Old 03-02-2009, 12:31 PM
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Quote:
Originally Posted by dirtinla
I understand how to wire up the 3 wire alternator.



The number 1 wire goes to a resistor or dash light and is suppose to glow when not charging. That wire goes to a dash light. The Dash light has 2 terminals one for neg and one for positive.

This is my question: Is the wire coming off the alternator + or - ? When I plug it into the light I need to know if the other connector goes to ground or hot (pos.),.

Thanx in advance as always,

-=Fred=-
The brown wire for the indicator light coming off the alternator is grounded when the alternator is not charging and provides +12V when it is charging. This wire goes to one side of the lamp. The other side of the lamp is hooked up to +12V battery power. When the alternator is not charging, the lamp gets the +12V from the battery and ground from the alternator, so the lamp comes on. Once the alternator starts charging the lamp now has +12V on both terminals, so it goes out.
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Old 03-02-2009, 12:51 PM
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Thanx for your assitance... I had to read thru a couple times to understand... but it makes sense.

Your explanation was invaluable rather than just stating the schematic.

-=Fred=-
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Old 03-01-2010, 07:57 PM
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I'm reopening this oldie - I had a similar concern as well today.

The 100 amp Powermaster (Delco design) alternator I have, 8-37100, has the capability to go either as a 1 or 3 wire. I'm currently set up as a 1 wire - and it works, but after doing my homework, late again, just like high school I prefer the better reliability of the 3 wire arrangement. The American Auto Wire schematic shows a red jumper from #2 terminal to the BAT terminal and a brown wire from #1 back a switched ignition position through a diode rather then through a resistor or indicator lamp. My question is will that diode create the proper resistance or do I still need a resistor - i.e. 1/4 watt, 10 ohm (or whatever is required) ? Or should I just go ahead and add a charge light along with the diode to prevent run-on? And last - do I really need #14 wire for that last wire - it will be a PITA at this point to run another engine compartment wire as I do have one spare #16, I believe.

Phew - I knew how to do the old external Ford regulators, and old dogs, new tricks.........

Dave W
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Old 03-01-2010, 08:22 PM
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The diode allows the current to flow in one direction only, but it does not provide any resistance. Every wiring diagram I've seen always used either the light or a resistor in the circuit.

14 gauge sounds pretty big for a wire that just provides a connection to the indicator. The stock wiring on my '75 truck with a 10si uses only 16 gauge wiring for the indicator wire. I used the same wiring and plug for terminals 1 and 2, and upgraded the charge wire to 8 gauge when I switched to a 94 amp 12si. Its run fine that way for several years.

Bruce
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Old 03-02-2010, 06:01 AM
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Quote:
Originally Posted by 75gmck25
The diode allows the current to flow in one direction only, but it does not provide any resistance. Every wiring diagram I've seen always used either the light or a resistor in the circuit.

14 gauge sounds pretty big for a wire that just provides a connection to the indicator. The stock wiring on my '75 truck with a 10si uses only 16 gauge wiring for the indicator wire. I used the same wiring and plug for terminals 1 and 2, and upgraded the charge wire to 8 gauge when I switched to a 94 amp 12si. Its run fine that way for several years.

Bruce
Thanks Bruce.
Yeah - I did know that about the diode, but there is a wee bit of resistance and wasn't sure if it was enough. I'll just wander down to Radio Shack and find a little resistor to use. My charge wire - bigger then #8, for sure is no problem, but that indicator wire -I'll use the #16.

Dave W
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Old 03-02-2010, 05:38 PM
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Quote:
Originally Posted by dirtinla
I understand how to wire up the 3 wire alternator.



The number 1 wire goes to a resistor or dash light and is suppose to glow when not charging. That wire goes to a dash light. The Dash light has 2 terminals one for neg and one for positive.

This is my question: Is the wire coming off the alternator + or - ? When I plug it into the light I need to know if the other connector goes to ground or hot (pos.),.

Thanx in advance as always,

-=Fred=-
If using an indicator light, you would use a single element bulb with a non-grounded (plastic) socket. It will have two wires coming from it. It does not make any difference which wire connects to the #1 wire coming from the alternator. The other wire from the socket connects to the ignition terminal on the ignition switch. When you turn on the ignition switch, current flows thru the bulb to the alternator (internally grounded) and will light up the bulb. Once the engine has been started the light will go out.

If you prefer to use a diode (not a resistor), you will connect it so that the current will only flow from the ignition terminal of the ignition switch to the alternator. A diode only allows the flow of current in one direction. The diode will prevent current from going back to the ignition switch and this will prevent a "run on" condition when the ignition switch is turned off. Use a Radio Shack #1N4001 diode or an equivalent value.

Speedway Motors offers an alternator wiring harness for the GM internally regulated alternator with the correct diode. Part #910-64100.

Alternator Harness

NOTE:

Whether you use a diode or an indicator bulb, the connection will go from the #1 terminal on the alternator thru the diode or indicator bulb and then to the ignition terminal on the ignition switch. The ignition terminal is hot only when the switch is in the ON position.

Last edited by Frisco; 03-02-2010 at 05:42 PM. Reason: added link
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Old 03-03-2010, 06:46 AM
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Frisco - thanks, especially for that diode number. I do have one in my wiring module, but to run another wire back to the area behind the seats where the wiring terminates and to keep it out of sight otherwise in a finished car - tough - so am planning on using the "spare" wire along with a new diode and either a resistor (10 ohm/1/4 watt) or light. I've already picked up the connector, but will file the Speedway information for the future (their new street rod catalog came yesterday - that part is on p174).

Dave W
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Old 10-09-2010, 09:13 AM
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diode

The speedway number is for the harness (plug and iwres with diode).
I have the diode only if you are doing your own wiring. See the classifieds.
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