3G alternator question

I've run into an issue trying to do a 3G alternator upgrade on my truck. The old alternator probably hasn't been charging for the five hundred or so miles I've driven this truck. It has new batteries and battery cables. I've got the alternator installed, removed the old regulator, and I have wired it up following some of the guides I've found here: Using the 3G pigtail, the white/black stripe wire is run back to the solitary plug, the yellow/white stripe wire is run to the post with the heavy gauge battery lead. The heavy gauge battery lead from the alternator is running through a 175A fuse. The truck starts just fine, but it isn't charging. I took the (new) alternator to the autoparts shop and had them check it - it's charging correctly. I haven't hooked the green wire up, as I read that is for the OEM voltmeter and I'll sort that out probably with an aftermarket gauge after I get the alternator functioning.

Here's a picture, for what it's worth, sorry it's so huge:


I hate having to make this thread to ask for help, as I'm sure this is a boneheaded error, but I can't figure it out. I've had a couple older and wiser guys look at it earlier and they didn't have any ideas.

Im pretty sure you have to wire the green up. It acts as an exciter to get the charging operation going.

Green wire has to be hooked up.

Either through the factory warning lamp, or if I understand it, it can be hooked to the ignition switch power.

Hook it to the lamp wire where the old reg was. I think its light green

take a volt o meter and test it running at the terminals. even my isspro reads lower than it actually is. it shows below 14 v with my driving lights, headlights, and ac on high. but at the terminal with all that load on or none it always reads 14.38V

The green wire is the wire that turns on the battery light in the dash at least that is how it is in my truck so I know 87-91 trucks are that way.

Terminal I has to be wired in for the alternator to charge.

Either through the charge lamp which acts as the exciter or to keyed hot with a 560 ohm resistor. So, find th charge light wire that went to your original VR and hook it up.

Thanks for all the help everybody, I'm heading out to the shed to find the wire in the factory harness and get it hooked up. The original harness has been pretty heavily modified by previous owners so I may end up just picking up a 560ohm resistor if I'm unable to locate the factory voltmeter wire.

I really appreciate the help!

FWIW, I don't like that lug on the charging power post.

when I put new lugs of this type on, I use a chisel and crease the center,

and with the insulation stripped about a 1/2" further back, I solder it, then weather proof shrink wrap.



Edit, do not think yours can be wired the same.
but keep all 12V+ exposure to a minimum

the rest of your connections look primo

If the regulator plug is still on the fender use the green with red stripe, it is to the batt light,and the correct way to operate the apt, very fail safe system. Less parts to fail.

I ended up using what appears to be a brown wire (I am partially colorblind so old faded wiring is the bane of my existence) that had been hooked up to the old alternator and I got 13.1V at the battery, at idle. My factory voltmeter still doesn't work, but I haven't opened the dash up yet and I'm fairly sure it has bad grounds already due to weird gauge behavior.

IDIoit: You're definitely right about the cable from the alternator to the fuse/battery. I was in a hurry when I had Napa make the two cables. I'll probably end up relocating the fuse and making up some new cables to replace the current ones.

Glad the truck is back in commission! What a great forum this is.

Does the batt light come on now? If not its still not right. Ground the old reg wires with key on till it comes on, then hook it to the green alt wire.

Does your truck have an amp meter?

I haven't seen a battery light - where would it be on the dash? I do have a factory ammeter (or voltmeter?) in the dash. It's marked "charge", and with the key on but motor off, the gauge is pegged to the left. When the truck is running the needle centers in the gauge.

The charge lamp is optional in your truck, you are decribing a voltmeter. There still should be a green with red stripe at the old regulator plug/harness. Basically as long as it is switched with ign switch you should be good to go. My friend that is colorblind says the green could very well look brown to him so you may have problem solved.