1 Wire Alternator

I’ve been working on the car over the winter, not driving it, but start it once in awhile while fixing things here or there. My battery died, and then would not hold a charge. Figured it was a bad battery as the charge would be gone as soon as I shut the car off. Bought a new battery. Same issue.

Just to be sure my solenoid wasn’t bad, I had another one laying around, I threw that on, same issue.
It has a new battery, new alt, and new solenoid.

I jumped the car to get it running, did the quick check of disconnecting the negative battery terminal, and the car died. Normally bad alternator I’ve heard a million times.

  1. I have a GM 1 wire alternator, and I have the ground connected to the negative battery terminal.
    I see some say no negative wire needed, some say connect that wire to the chassis, some say to the negative battery terminal.

  2. I ordered a new alt in the meantime, maybe my Autozone special is fried.

Do I need to connect a ground on the alt?
Is there any other place I can look in the meantime, fuse etc? (I do not have a fusible link from alt to battery) I’ve looked at the underdash fuses, do not see any blown. Or any other ideas?

Thanks in advance

There’s no ground needed. The alternator needs one wire - hence the name. The alternator bolts to the engine. The engine is the best ground ever. The negative battery cable is connected to the engine.

Disconnecting the battery cable with the engine running proves you have no idea how to work on alternators. This stunt normally will fry the diode(s) in an alternator. Don’t do that.

If you have an alternator that needs testing, measure voltage at the battery with the engine running. If the alternator is good you will have 13.7 - 14.2 volts.

A one wire alternator is not a bad thing, but you need a voltmeter to monitor it.

You are right, I am limited on my alternator experience, hence the post and questions! :stuck_out_tongue:
I understand how the alternator bolts to the engine, negative cable to the engine, etc, which is why I was wondering why the alternator has a ground post on it. If it is already grounded via being bolted to the engine, why the ground post terminal on it?

You answered one of two with sarcasm, want to jump on the second question and bat 1000? :smiley:

Is there any other place I can look in the meantime, fuse etc? (I do not have a fusible link from alt to battery) I’ve looked at the underdash fuses, do not see any blown. Or any other ideas?

Some factory wiring harnesses might have a ground wire to connect to that alternator in liew of having what your car had from the factory - a ground wire connecting the RH cylinder head to the body. This is not for the purpose of charging the battery, it is to ensure that things like the instrument panel have a good ground. It’s not your problem. You do need a connection between the body and the engine for best results.

One wire alternators typically have to reach a “threshold” RPM to begin charging. Typically it is around 1500 RPM. You will need to connect a voltmeter to the alternator and watch it with the engine running. Or take the alternator to Auto Zone or any other decent auto part store for a free test.

Thanks Royce,I see on the PowerMaster starter and alternator website, that if your alt bracket is painted, then there may not be a good ground to it, a ground wire should be run to the engine/chassis, I guess that is what mine has, a “backup plan” for the ground.

Alternator Ground: Many mounting brackets are
powder/clear coated, painted, or plated. The
alternator will not ground properly without a ground
wire from the Alt. housing to the engine block. (This
wire should match charge wire size)

I’ll take it off and to Auto Zone tonight, appreciated!

One wire alternators are not necessarily bad, particularly if you get a real one made back in the day by Generic Motors.

The problem is that many are made of 100% Chinesium, with quality and design compromised by efforts to make the product as cheaply as possible. You need to watch out for the ones that sell for $69 with no core required. You get what you pay for. Personally I can’t find a problem with original Autolite alternators, particularly when paired with a good quality Motorcraft electronic regulator.

That my explain it my friend, this alt was probably $79 from Autozone/Advanced I believe. The ordered one from Summit, and the wiring bolt/nut was on the top rear left, and hitting the head, I couldn’t get it to mount. My options were to get a bigger belt and bracket, or get an alt that the wiring bolt/nut was on the bottom for clearance issues. I opted for the latter and a cheaper alt I could look at the back in person (the majority of the ones on summit didn’t show the back) and make sure it would fit.

I put on a new harness, and have the alt connector/regulator connector still attached, if this alt is spent, your setup sounds like it would work perfectly on mine as well. Recommend a place to buy a quality Autolite alt and Regulator? I know of a couple of places, but always up for a recommended place first.

most of these older alternators you can “clock” the case to the right position for your application.

Correct me if Im wrong but I think you may run into an issue with the original style alternator if you have a high electrical load demand with accessory’s. The original alternator has a relatively low amp output if I remember correctly. In a stock application it would be just fine but if you need more power you may want to upgrade to a higher output setup

100 amps at idle - 150 amps at cruise.


The alternator should ground through the bolts to the engine, but if you get a fancy painted one with powder coated brackets, etc. it doesn’t always ground line it should. I did the one wire and added a ground cable to the engine block just for good measure.

It’s very easy to tell if an alternator is charging with a multimeter, and any local parts store can bench test it. No need to yank the battery cable.

Tested the alt with a multimeter, was reading 12.45 at the battery. Figured the alt was bad. Took it to Advanced, they tested it, it came back good. I am going to run a new wire from the alt to the solenoid, see if that is the issue. I’m going to see if I can get a reading directly from the alt instead of the battery terminal as well.

This alternator should be capable of 100 - 150 amps. When connecting it to the battery you need some seriously big wire. The ends need to be soldered and crimped. Unless you already own the tools for such fabrication it is normally cheaper and easier to just buy the proper size:


I would not use any type of fusible link between the alternator and the battery but if you are capable of installing one it won’t hurt anything. You can also buy pre-fabricated wire with a fusible link inline.

All of this oddball stuff makes the car harder to service and maintain, which means any failures on the road become events that take days to recover from.

That is could be the issue then. Looking at the wire the PO of the PO had installed, it is 8-10 gauge at best, with the cheap arse crimp on electrical eyelets and electrical tape.

Crazy how some people take care of their car in some areas, but others they half arse it with cheap parts/quick fixes. PO put on a new top, paint job some years ago, but Dollar General electrical connections and fabricated hose attachments and vacuum openings on the intake manifold.

Thanks for the link, I will keep you posted, working on it again after work today.

Thanks Royce, appreciated.

There ya go, perfect solution to get more amps if needed. Ill keep that in mind if I get to that point. Thanks royce.

battery cable condition, size and cable ends are very important, Make sure everything is clean and tight. I just had an odd issue on a work truck the other day. The lift-gate wouldn’t function but everything was hooked up correctly and everything appeared to be fine. Testing the cables found a terminal end corroded up inside the wire just enough to reduce current flow enough to stop the lift-gate motor from operating. Quick visial everything looked fine until taking a closer look at the cable connection and condition.

You can buy premade cables but they tend to be the wrong length so I suggest making them(ebay link royce posted might be a good option for correct length).Its a small investment to get the crimper, ends and shrink tube and you can make your own whenever you want.

I saw harbor freight carries these now too. I have a version of this along with a $300 set of crimpers. This cheap hydraulic version is easier to use in tight places and crimps just about as good.

Great! I always like to try and learn to make/build it first, so I’ll get a set to add to my collection of tools I’ll use once in a blue moon! lol Will come in handy, I appreciate it Royce and DieselD!

Be aware, the alternator can bench test good but still have bad diodes. Had that happen and went a few rounds with the shop before they finally replaced it under warranty.

No dice. Like Jetexas said, alt bench tested good. I put it back on, ran a bigger new wire from alt to solenoid, and made sure my positive cable ends were good.
Was at 12.45, now at 12.50.

I connected the multimeter directly to the back of the alt, same reading.

Guy at Autozone said it should be putting out 14-15 ish at idle.

I have a new alt from summit waiting in the garage, gonna throw it on when my frustration subsides and I get back on it in a few.

Success. Trash alternator from Advanced Auto. Put on the one I got from Summit and am getting 14.65 at the battery. Like someone said, get what you pay for! Thanks all for your help!

Is it a Summit “brand” alternator? If so, keep an eye on it as well.