Revisiting the alternator resistance wire

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pagrunt

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Sep 14, 2014
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This has came up a few times in the past with converting to factory gauges. I know the Pontiac guys reallyhave no issue with it as their volt gauge has a warning light in it. From the time my Monte was on the road (& still assembled) after I did the conversion ('93 to '10) the car never had a charging issue with out using the resistance wire (130) that ran from the bulkhead connector to the Ignition 3 (300) on the ignition switch. It just had the circuit (25) run complete/unaltered to the cluster plug where the wire still sits at this point. I have a doner harness that has it in it & wonder if it'll be worth it to add it in, leave it be, or convert the Check Engine light into a alternator warning light. The other thing is what real purpose does it serve if I'm not having any issues with out it. Does it keep the volt gauge from flicking when the turn signal are on (seen this on conversion & aftermaket gauges). Despite everything I've learned over the near 29 years having the car, that wire/circuit I don't fully understand it's purpose.
 

79 USA 1

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Sep 2, 2011
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Cheektowaga, New York
For what it is worth.....
I've done 2 conversions from warning lights to gauges in my 79 Monte Carlos. I have always ran the 10 ohm wire from the bulkhead connector (Replacing the #25 wire) to ignition 3. You do not have to disconnect the #25 lead at the dash "harmonic" clip due to the fact there is no connection to the printed circuit at that point. I was told the 10 ohm wire is used as an exciter for the voltage regulator in the alternator and without it I may run into charging issues. While working at the ignition switch wiring I also remove and securely tape the dark green wire from the start/ground test (Circuit#35) to keep the temp gauge from pegging full hot while cranking the engine.

I did the first 79 back in 1988 and have not had any issues. This past winter I did the blue 79 in my avatar and again no problems.
:popcorn::popcorn::popcorn::popcorn:
 
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pagrunt

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Sep 14, 2014
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That's good info. I never thought too much about the temp gauge pegging with the cranking of the engine but I'm on the fence for adding a warning light with the gauge. Back to the #25 wire, as stated above I do have a salvage harness with the correct resistance wire intact in it to use. Who knows I might get lazy & repin it to the CEL spot in the connector & turn that into my "Gen" light.
 

79 USA 1

Royal Smart Person
Sep 2, 2011
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Cheektowaga, New York
Its hard to get a good shot of the wiring diagram I used from the 79 manuals but, the #25 circuit becomes the brown wire on the alternator on the engine side of the bulkhead. The warning light bulb would supply the resistance to excite the regulator to work. The 10 ohm (Circuit #130) wire plugs in place of the #25 circuit inside the car to deliver the resistance to the regulator. I like the idea of using the CEL as a back-up!
 

pagrunt

Geezer
Sep 14, 2014
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Elderton, Pa
I have wire diagrams for '78-'81, '83, '87 so I can compair changes that could affect my rewiring. Odd thing in the '83 Electrical Troubleshooting Manual shows the temp gauge with the same wire going to the ignition switch like the warning light. Then again GM uses "gage" instead of "gauge" in the manuals.
 

Ribbedroof

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Jan 4, 2009
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Who knows I might get lazy & repin it to the CEL spot in the connector & turn that into my "Gen" light.

FWIW, that's what i did on my coupe...keeps the resistance in the circuit, and serves as backup in case I miss the gauge being low
 
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Ribbedroof

Comic Book Super Hero
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Jan 4, 2009
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I couldn't find a clear spec for the resistance wire (10 ohm....per???inch, foot, meter, ???) and really couldn't find any via google , and haven't seen an OE gauge harness in years in a yard. Since there's no ECM in my car, I figured the CEL was a great place to go with an indicator, and would work as original.
 
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