Jim_PA

iTrader: (9)

I had a 3-wire alternator setup when I was SBC --

One wire from battery to the post on the back of the alternator.

Second wire spliced from battery wire to one side of alternator plug.

And a 3rd wire that just goes up into the wiring harness from the other side of the alternator plug (I'm assuming for the GENERATOR light??)

ON THE NEW Alternator....

Battery goes to post on alternator (duh).

Then there's 2 wires going into the new engine harness through the 4-pin plug.

Do I need to do anything with the wire that disappears into my old trucks wiring harness, or does that just get eliminated?

Anything else I need to do? I did read Thee! Alternator FAQ, but I'm still not sure.

Thanks

Jim_PA

iTrader: (9)

has anyone here ever swapped out their GEN1 SBC for an LSx?

gofastwclass

iTrader: (2)

Hahahahaha!!!! Nope. I bet no one has ever done that.

FastKat

iTrader: (10)

What year/model engine, PCM and wiring harness are you using?

Jim_PA

iTrader: (9)

2004 LQ4, Silverado 2500, wiring harness and pcm from same. Thanks!

bovey

Hey Jim,

I'm running a 427 LSX/Big Stuff 3/T-56 Magnum combo in a "71 GMC and I'd love to help you out, but I'm having a charging issue, so I'm reluctant to give you advice until it sorted, but I will unless someone beats me to it.

One thing I would reco is to be diligent and carefully remove/tie-up the old wiring harness to make sure there are no glitches like I have. I thought we were careful, but as it turns out, not careful enough.

You're gonna love having the LS in that thing, mine is a riot.


Cheers,
Bovey

downset71

you can basically separate alt. harness from ECM harness.....just like old setup, one wire will jump rite over to constant BAT+, and other will goto dummy light in dash or you can run it through(in series) a small bulb and out to IGN+ ( so it will charge). depends on make of donor harness which wire will do which job. colors are usually differant.....so search on forum for more info

FastKat

iTrader: (10)

Jim,

I've seen this exact issue discussed before on different threads - you can probably find it if you so a search titles only for "alternator".

The brown wire from your alternator (terminal B on the alternator's wiring harness plug) can go through a resistor, and then a dash light, and then to a B+ circuit... preferably one that is fused with a key. This is your alternator trouble light. I believe you need to have some resistance in this line to keep your alternator from burning up in the long run. The dash light should give you some resistance. The total resistance on the circuit should be about 470 ohms. The normal fix is to solder a 470 ohm 1/2 watt resistor inline on this wire... that's what I did.

As for the grey wire on the alternator plug (terminal C) I don't know what it does... but I know it's been discussed on this board before.

Jim_PA

iTrader: (9)

I was mainly worried about the "extra" connection on my old alternator. It turns out after doing some digging that the mystery wire is going to ground, and serves no purpose even in the current configuration.

On my new one (for those that may find this in the future, and can't figure it out...)

1) Battery to post
2) White wire from alternator plug (labeled F on back of alternator) to Key 12v+
3) Brown wire from alternator plug (labeled L on back of alternator) to 470 ohm 1/2 watt resistor then to Key 12v+

Thanks for the assistance everyone -

bovey

glad you got it sorted out.

Same solution as mine. So simple, that reward 20/20 vision can be annoying.

Good luck with your build.

Bovey