Alternator dilema

[LeesTruk]

Didn't want to hijack TBrown's posting on alternator issues, so I'll start my own, and I don't mean to drag up a continuing alternator problem...

Anyways, My truck is a '80 C10, w/5.3l from a '05 Tahoe, using the DR44g alt. The truck has been running now for about 4 yrs. with no electric concern, other than the 13+ volt output. After reading Tbrown's question about resistors on the exciter wire (brown wire), I was curious. With key on, exciter voltage is 10vdc, battery voltage is 12.7vdc. So. I checked my wiring, brown wire to C2 pin 15 (gen. control), grey wire to C2 pin 75 (duty cycle signal). Both check good continuity. From searching here, a past posting from DAYj1 on this subject shows a mod that can be made to the DR44g, but also, a schematic for the gen III LS in trucks. The schematic shows that a third wire, C1 pin58 (serial data to the IPC) is used in the charging system. Is this needed for the PCM to allow proper charging? If not, would a resistor added to the brown wire allow my alt. to charge properly? If it's as simple as adding a resistor, then I'll do that .

[thehata1]

I am confused. I thought one would want the alternator to put out more than 13 volts. If not, I have a problem, as well. Subscribing

[LeesTruk]

Don't be confused, man. You do want 14vdc or better! Apparently later genIII LS's, and beyond, have alt's that are regulated via the pcm, bcm, and the generator battery control module or gbcm. When the alt. doesn't have ALL of that hooked up, it defaults to just over 13 vdc all the time (my situation). This alternator thing has been going on for quite a while here on the site, and elsewhere apparently. Even after my truck has been together for some time, I'm still learning new things. Just buying an aftermarket harness and plugging it in does not guarantee a perfect solution. From what I've read so far (been all day researching this, shudda stayed dumb and just accepted the 13vdc output), I've either got to modify the DR44g, or change to an earlier style AD244, unplug the harness from the alt/pcm, and rewire the alt. to accept a switched 12vdc source with a resistor added to it ( I might have answered my initial question?) Hopefully. I'll get some kind of response

[derotoreut]

I had no idea about this. I just completed my first LS swap with a Gen III 5.3L LM7. I noticed the alternator output at around 13.7 V and wondered, what the heck? I'm going to have to go back and search out some of these threads. By the way... what is the DR44g alternator? As far as I know there are two styles, large case and small case. Mine is the large case alt.

[LeesTruk]

Don't think you are alone with this! I think there are a lot of tinkerers like us that don't fully "know" their way around the LS charging system. The Dr44 and DR44g replaced the AD244 (large body) alternators I guess around late 2004-2005 period. You'll have to do some research on the why's of the change, along with the voltage regulator control being controlled by various modules and pulse width modulation. I've spent much of the day today reading posts on this site, going back as far as 2010. This seems to be one of the little known facts about the LS swaps. Back in 2015, when I put my truck together, I thought I had it pretty well figured out. Here it is 5 yrs. later and I'm Still learning!!

[Richard]

Originally Posted by derotoreut

I had no idea about this. I just completed my first LS swap with a Gen III 5.3L LM7. I noticed the alternator output at around 13.7 V and wondered, what the heck? I'm going to have to go back and search out some of these threads. By the way... what is the DR44g alternator? As far as I know there are two styles, large case and small case. Mine is the large case alt.

You are good to go IMO. When is the last time you had the testing device calibrated? .3v from 14v on a multimeter I would not worry about. If you used another it may read + or -

[ls1nova71]

The GBCM was introduced on trucks in 2005 as a way to increase fuel economy by not having the alternator charging at full potential all the time. Prior to that, there were just two wires going from the alternator to the PCM, and the PCM controlled the charging. I have in the past had a 2006 swap programmed like 2004 and wired it as a 2004 also and it worked perfectly, although that did require a 2004 TAC module too since they have to be matched to the tune. However, it has since been figured out that you can just leave the GBCM on the battery cable and wire it accordingly, but without the wire going to the BCM and it will work. Here's a thread on the topic. https://ls1tech.com/forums/conversio...le-gbcm-2.html

[LeesTruk]

First off, thanks Nova, the info was helpful. So, because I'm a hoarder of sorts, I still have the original harness from my engine package. I checked it, and the GBCM pigtail is still there, but no module. So I got to thinking, because I'm gonna put an '04 regulator into the '05 alt., why can't I wire it like the old days and CS series alts. I'm thinking that the exciter feed from the PCM is resisted (reading 10vdc at the pin)not B+, why couldn't I just attach what was the duty cycle wire from the PCM, to the B+ post on the alt. to sense voltage load, and let the regulator do its' thing when the demand is needed(wire from the alt. pigtail, not the PCM), not just achieve a constant output, no matter what. Any thoughts?

[DM72C20]

In the same boat with my swap: 09' Silverado Gen 4 4.8 donor motor and trans into 72' C20.

I am planning to use the GBCM and have it in place on the negative cable. Computer and wiring are all from the donor truck and modified as needed.

I thought I had it figured out after reading the tri-five thread about using a PWM controller to alter the signal to the alternator. I picked one up for $17 figuring it wouldn't be the end of the world if not needed. Reading this thread and Nova's reply makes me think that the PWM gadget isn't needed now..

In the ls1tech link I read this from Hart Rod: 2 wires to the alternator, 2 wires to the battery, 2 wires to ground, 1 wire to serial data port - BOOM!!, it works!!!!

Not too sure where that serial data port wire needs to be connected?

[Duck1]

Originally Posted by LeesTruk

Didn't want to hijack TBrown's posting on alternator issues, so I'll start my own, and I don't mean to drag up a continuing alternator problem...

Anyways, My truck is a '80 C10, w/5.3l from a '05 Tahoe, using the DR44g alt. The truck has been running now for about 4 yrs. with no electric concern, other than the 13+ volt output. After reading Tbrown's question about resistors on the exciter wire (brown wire), I was curious. With key on, exciter voltage is 10vdc, battery voltage is 12.7vdc. So. I checked my wiring, brown wire to C2 pin 15 (gen. control), grey wire to C2 pin 75 (duty cycle signal). Both check good continuity. From searching here, a past posting from DAYj1 on this subject shows a mod that can be made to the DR44g, but also, a schematic for the gen III LS in trucks. The schematic shows that a third wire, C1 pin58 (serial data to the IPC) is used in the charging system. Is this needed for the PCM to allow proper charging? If not, would a resistor added to the brown wire allow my alt. to charge properly? If it's as simple as adding a resistor, then I'll do that .

The resistor is a used in carburetor applications or where they brown wire is not going to ECU. You use a resistor or the dash light bulb