69 GMC C1500 Stepside Alternator Issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**BuilderBee** · 01-06-2025, 07:28 PM

Replaced alternator and voltage regulator on my 69 GMC (250 4.1L engine), generator light stays on, voltage coming from battery is reading at 12 volts, if I am correct alternator should be showing over 13 volts to ensure battery is being charged. Correct?? I checked all the connections, battery is fully charged and well maintained. Appreciate any info as to why my generator light stays on.

**1970cstblazer** · 01-06-2025, 07:37 PM

Was it charging prior? Running voltage should be 13.5-14.2, dependent on battery condition, engine speed, and ambient temperature.

**Steeveedee** · 01-06-2025, 07:38 PM

Minimum voltage for the charging system is 13.5 Volts. It is not charging. Is this identical to the case before the alternator and regulator were replaced? BTW, a batter at 12V is basically considered dead. It should be at 12.6V to be considered fully charged. Can we see a picture of your setup? Here is a wiring schematic for your truck. Never mind that it shows a V-8, the charging circuits are the same.

**BuilderBee** · 01-06-2025, 10:35 PM

Quote:

Originally Posted by 1970cstblazer

Was it charging prior? Running voltage should be 13.5-14.2, dependent on battery condition, engine speed, and ambient temperature.

Original alternator was tested twice and showed not charging and needed to be replaced. Replaced with new remanufactured alternator from Rock Auto Parts and new voltage regulator as a precaution had remanufactured alternator tested and it is in working order. Battery has been well maintained and I ensured that it was fully charged after installing the new alternator.

**BuilderBee** · 01-06-2025, 10:40 PM

Quote:

Originally Posted by Steeveedee

Minimum voltage for the charging system is 13.5 Volts. It is not charging. Is this identical to the case before the alternator and regulator were replaced? BTW, a batter at 12V is basically considered dead. It should be at 12.6V to be considered fully charged. Can we see a picture of your setup? Here is a wiring schematic for your truck. Never mind that it shows a V-8, the charging circuits are the same.

Hi Steven,
Thanks for the wiring diagram, Original alternator was tested twice and showed not charging and needed to be replaced. Replaced with new remanufactured alternator from Rock Auto Parts and new voltage regulator as a precaution had remanufactured alternator tested and it is in working order. Battery has been well maintained and I ensured that it was fully charged after installing the new alternator. On a side note I see that you live in Simi Valley. I live in the San Fernando Valley. With respect to photos I will need to take some and upload.

01-06-2025, 07:28 PM	#1
BuilderBee New Member Join Date: Jul 2023 Location: Los Angeles, CA Posts: 9	69 GMC C1500 Stepside Alternator Issue Replaced alternator and voltage regulator on my 69 GMC (250 4.1L engine), generator light stays on, voltage coming from battery is reading at 12 volts, if I am correct alternator should be showing over 13 volts to ensure battery is being charged. Correct?? I checked all the connections, battery is fully charged and well maintained. Appreciate any info as to why my generator light stays on.

01-06-2025, 07:37 PM	#2
1970cstblazer All stock and staying that way Join Date: Jul 2003 Location: Elkland, PA Posts: 1,883	Re: 69 GMC C1500 Stepside Alternator Issue Was it charging prior? Running voltage should be 13.5-14.2, dependent on battery condition, engine speed, and ambient temperature. __________________ 1970 K/5 Blazer CST 4WD, TOTM winner December 2024! Medium Bronze, 93k ACT. miles, 350, 4 speed, rear positraction, 16.5" x 8.25" HD wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration finally getting close to completion.. 1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor... 2017 Sierra 1500 SLT 4WD, Black, 45k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2... 2019 Canyon SLT 4WD, White, 62k miles, 3.6, 8L45, 3.23 LS, 18" wheels

01-06-2025, 07:38 PM	#3
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,736	Re: 69 GMC C1500 Stepside Alternator Issue Minimum voltage for the charging system is 13.5 Volts. It is not charging. Is this identical to the case before the alternator and regulator were replaced? BTW, a batter at 12V is basically considered dead. It should be at 12.6V to be considered fully charged. Can we see a picture of your setup? Here is a wiring schematic for your truck. Never mind that it shows a V-8, the charging circuits are the same. Attached Images __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA



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