On the 99-02 PCMs the red connector, pin 15 connects to the alternator pigtail. In a factory setup does it go from pin15 to a incandescent cluster dummy light, THEN to the alternator, or does it run from pin 15 straight to the alternator?

If it runs from pin 15 straight to the alternator, then how is the alt dummy light handled on a 99-02 fbody?

I'm trying to decide if the wire from pin15 needs to see some resistance, whether thru a resistor, or an incandescent bulb, before it gets to the alternator.

 

It runs directly from pin 15 to the alternator. The idiot light is run from the PCM via serial data.

 

99 and 00 are different from 01 and 02 on the trucks. See attached gif image

I found this thread earlier that may help you out. https://ls1tech.com/forums/14588749-post87.html

 

Do you have any diagrams or sources that support that?

I've just read so many different ideas on the subject that Im looking for a little more proof.

Once the purple serial data wire (blue connector pin 58) makes it into the cabin, where does it branch off too before the OBDII port? Something has to be decoding the serial data signal then controlling the alternator light in the gauge cluster...?

 

You must have posted while I replying to G-body.

I believe your attachment on the left would be like how the fbody setup works, minus the pin numbering being different, etc.

Looks like the "logic" to decode the serial data stream is in the cluster, I guess that answers my question to G-body a bit.

The diagram in your link does not appear to be correct for a 98 or 99-02 fbody setup. The fbodys only use one pin on the pigtail, not 2.


So would I be wrong in thinking I can just do as attached and have it work correctly? IE, the alternator gets the right "exciter" signal, and the LED would illuminate if the alternator pin B sunk to ground in the event of an alternator failure, in turn lighting the LED due to the other side of the LED seeing + from pin R15? Eh?

 

I could be wrong but I don't think its that simple according to post 6 here from Speartech. https://ls1tech.com/forums/conversio...-question.html

Honestly I would ask them. They specialize in this stuff and do it every day.

 

I know you need a incandescent light or resistor between a direct power to alternator deal, thats no question.

The main thing Im trying to verify is that the 99-02 pcm drops the alternator wire to the correct voltage on its own and does not rely on a dummy light or resistor to drop the voltage.

As G-body points out, the 99-02 pcm pin R15 goes to the alternator, and does not go through a dummy light. Im inclined to agree hes right, but that doesn't rule out the possibility of a resistor being wired in from GM somewhere inline from the pcm to the alternator.

I am in a bit of a unique situation, this is a swap application, and I started with a 98 harness, which I repined to use on a 99-02 PCM. I have built the 99-02 style alternator charging side of the harness from scratch. I'm kinda looking to hear from someone who has torn down a 99-02 harness and visually traced the wire that runs from R15 to pin B on the alternator to let me know that there is for sure no resistor wired in. Then I can safely assume that the PCM varies the resistance to the wire running to pin B on the alternator.

Someone can check the voltage (edit: voltage, not resistance*) of the wire running from R15 to Pin B just after the PCM connector, and just before the alternator so I could compare the values, but I don't think anyone is going to jump head over heals to do that for me

 

Again I would call some one like Speartech or PSI as this is exactly what they do on a daily basis.

 

Ya, I just hate calling to ask a question when Im not buying anything ha. I do need to order a few things from EFI Connection, maybe I'll give them a ring this week.

 

I just pulled up the cluster diagram and I don`t even see a alt light shown in the cluster. I attached the diagrams for the instrument cluster and alt.