Ground wire from alternator? (1 Viewer)

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Aug 16, 2014
North Texas
I'm wondering is there supposed to be a ground coming off the alternator somewhere to the engine block? I read somewhere that there is and I don't seem to have one, at least not to my untrained eye.

I do have this tho. A broken connector still attached to one of the bolts on the alternator bracket.

ImageUploadedByIH8MUD Forum1422501894.872172.jpg

Also, if it should have a ground and doesn't, what kind of problems would it cause?
As long as the part in question (alt) is grounded through it's case to the engine , and the engine itself has a good ground to the battery , all should be good . But , in many cases , over time those connections get corroded , just like the battery cables . I usually run one heavy ground to the starter mounting ear , and another one that's a bit lighter to the alternator case or bottom mount . Stops a lot of charging issues so the alt can read the current in the system and not hunt for a ground for it's field .
Rudi explains this stuff better than I can , he'll be along in about 3,2,1....
3,2,1....... 1 day and 2 hours late but here I am.

The body of the alternator is ground. The alternator is mounted on the engine and the engine should have a ground strap to the frame.
From the frame there is a ground strip to the battery. That's a long way for a ground circuit. Works fine when the truck is new but after 30+ years you'll have all kinds of corrosion on metal parts.
There is a tiny ground wire on the alternator but that one goes to the voltage regulator to make sure that there is no voltage difference between the firewall where the VR is mounted and the body of the alternator.

Personally, as an electric guy, I don't like the series ground circuit: -► battery -► frame -► engine -► alternator.
To avoid ground problems I'll advice to make a "star" ground circuit where the battery is the center of the "star".
Battery to frame, battery to engine (as close as possible to the starter motor) and battery to body (preferable to the VR housing).

I think that a PO had a ground problem and tried to solve it with a ground wire to the alternator. That's what I see in your picture.

sounds familiar on top of the stock ground from starter bolt to frame i always added one to the alternator mount from the battery .seems like about a 10 year span here and you have to take that stuff apart and clean it all or you have problems
Yep, I always suggest a separate ground wire to the CASE of the alternator. There have been many problems with powder coated or painted brackets not allowing the case to ground properly. The alternator then tries to pull current through other grounds, resulting in a burned up ground system. Either scrape the brackets to bare metal, or install a ground strap to the case!
Ok. Thanks for the replies. If this is a problem would there be any noticeable symptoms that I should be looking for? I feel like my alternator is on its last leg anyway.
Sounds like the bearing on the pulley is going out. It makes a lot of noise. The amp gauge on the dash works and any time anything is on there is a significant drop in the gauge. Like when the blinkers are on the gauge drops and rises with the blinkers. The more load you put on it the more it does.

Hope that helps.
Yep, that's what the Ammeter does. Showing how much drain there is but..... it also should go positive indicating that the alternator is charging.
What's the voltage on the battery at let's say 1200 rpm? Voltage should be in the 13.6 - 14.4 range and the Ammeter should go positive.
Same question but now with the headlights on. Voltage should be minimum 13V.

Battery stays around 12. Head lights on drops it to 11.93. Hard to check the RPM with just won set of hands.
Headlights on:

ImageUploadedByIH8MUD Forum1422590151.828813.jpg

And off:

ImageUploadedByIH8MUD Forum1422590170.945801.jpg

It stays in that position and doesn't raise back up.
Battery stays around 12. Head lights on drops it to 11.93. Hard to check the RPM with just won set of hands.

How about: pull your hand throttle a bit?

You can tell I'm fairly new at this. How can something so obvious elude me? Ha

I will check that tomorrow. Thanks Rudi.
Ok, so while running with normal idle it's showing 11.99. At about half throttle and full throttle is showing the same. I'm thinking it's not working right. Ha
Yep, it's not working but the big question is WHY?
Is it the Alternator or the Voltage Regulator? 50/50 chance.
On the VR you'll find 3 wires.
* Red/Yellow stripe (on some models Black/Yellow stripe). This is the IGN wire that should be 12V when the key is in the ON position.
* White/Green stripe. This is the Field wire. This wire should be around 12V as long as the battery is below 13.6V.
This wire "regulates" the output from The alternator.
* White/Black stripe. This is the ground wire. Not important at this moment.

If R/Y is not 12V you have a wire problem between the "engine" fuse and the VR. Maybe a bad contact if you're lucky.
If R/Y is 12V but W/G is not 12V you have a defective VR.
If W/G is 12V, and still no output on the have a defective alternator.

Thanks Rudi. I will work on it this afternoon. Hopefully soon I will know which is problem.

Let me ask you this. Could this problem be causing other electrical problems because of the lack of needed electricity?
Went to check those wires this morning and I noticed this.

ImageUploadedByIH8MUD Forum1422810698.183106.jpg

I must have left it unplugged a couple of weeks ago when I was checking those wires before. Regardless, I should have noticed that.

I will check again with it plugged up and post those results.

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