[Zoomad75]

Here's the thing, if you are using the stock harness from the 5.3, the alternator should charge normally as the PCM is controlling the field duty cycle. Problem is, the gen light on the stock 5.3 setup is not a direct wire function to the cluster. On the stock silverados, the pcm sends a signal to the cluster via class 2 communication to turn the light on if the system voltage drops below 11v or over 16v. Meaning, for a stock old truck cluster the pcm can't control the light.

You are better off converting your truck to single wire, non externally regulated setup. Like I said before, we tried to make mine work and it behaved weird. It would start charging on initial start to stop 30 seconds in. Pulling off to get it tested off the truck confused matters more. It tests fine. Put it on the truck and it goes back to charging for 30 seconds and stopping. The kicker is the regulator is not getting a straight voltage from the pcm it is pulse width modulated up to 400 cycles a second.

So you have a choice, used the stock 5.3 alternator with the pcm controls without the gen light or ditch the pcm controlled alt and go with the single wire setup that will run the gen light correctly.