Generator light with 5.3 alternator

[qwik]

I'm wiring my 5.3 swap, is it possible for the generator light to work correctly with pcm wiring controlling the alternator?

[Zoomad75]

We struggled getting the alternator just to charge much less work the gen light on my swap. This problem was most likely caused by multiple issues in my case. The MEFI4 system I'm running does not control the charge output of the alternator. Second, the alternator came with questionable history as a used part from a training center.

Efforts to wire it up as a stock alternator and make it work failed. Frustrated we ditched the questionable alt and went with Larry's tried and true alternator of choice. We used the CS144 delco unit. Available just about anywhere, but I used NAPA. Best part is the 140amp output, non-computer controlled and fits right in where the stocker got ejected from. Wire it up like a stock alternator, heck I even used the stock plug for the 91 alternator for it. 140amp output is way better than the stock stuff too!

[qwik]

I'm using the 4 pin gen 3 alternator. My question is, is the I/F terminal a switched 12v from the pcm or should it be disconnected from the pcm and connected to source from the truck? Also the L terminal (alt turn on) should be a 12v source with a 500ohm resistor or gen light, I'm assuming I should disconnect the brown wire from the pcm and connect it to brown wire that previously hooked to my voltage regulator.

[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.

[qwik]

So you're saying the alt. (5.3) will not work correctly with an independent 12v source to the I/F terminal and the brown gen light wired directly to the L terminal?

[Zoomad75]

Originally Posted by qwik

So you're saying the alt. (5.3) will not work correctly with an independent 12v source to the I/F terminal and the brown gen light wired directly to the L terminal?

Yes, I'm saying in my case we could not get the 5.3 alt to work with a 12v source to the L terminal. You can make it work with the stock 5.3 wiring harness you just won't have the gen light working.

[MalibuSSwagon]

My 2 cents, if you are using a stock PCM and harness leave it the way GM designed and convert to a square body voltage gauge like LS1nova71 did. Why undo all this to have a functioning idiot light?

[qwik]

Originally Posted by MalibuSSwagon

My 2 cents, if you are using a stock PCM and harness leave it the way GM designed and convert to a square body voltage gauge like LS1nova71 did. Why undo all this to have a functioning idiot light?

I see your point, but my truck has a clean 3 hole cluster that I'm sorta hung up on using.

[ls1nova71]

If you are good with electronics, or know someone who is, (I definitely am not) I'm sure there is a way to build a circuit that will turn on a light when the voltage drops below a specified value, say 11v or so, and turns off when above it. May not be 100% like factory, but would give you a heads up that the alternator wasn't charging. Just a thought

[qwik]

Originally Posted by ls1nova71

If you are good with electronics, or know someone who is, (I definitely am not) I'm sure there is a way to build a circuit that will turn on a light when the voltage drops below a specified value, say 11v or so, and turns off when above it. May not be 100% like factory, but would give you a heads up that the alternator wasn't charging. Just a thought

I've thought about that also. I believe a low voltage disconnect would work, I've seen 12v ones that open a circuit at 10.5-11v and are fairly cheap.