M1028 Gen 1 Light On

I'm looking for some advice on the next step I should take troubleshooting a Gen 1 light that is staying on in my M1028.

The light came on two days ago, so I followed the TM and ended up replacing the alternator. I used the Duralast alternator listed in the wiki. Light went off for about 6 hours, at which point I realized that the old front battery had popped after the light came back on. I replaced the front battery, but the Gen 1 light still has a dim glow to it that does not go out if you rev the motor, but does get brighter the more things you turn on.

I checked the voltage on the system, and am getting 12.5V on the front battery with the system off, and 14.5V on the front battery and 14.6V at the alternator with the system on. It seems like the system is actually charging, but my light won't go out for some reason. I haven't had any issues with the Gen 1 light prior to this either.

I've already looked through pertinent threads to try and find some answers or other things to try, but haven't found anything out of place yet. Does anyone have a good point to start with?

Thanks in advance.

There is part of the alternator that activaites the idiot light. I don't know what the part is but when I have issues I take it to an alternator shop and puts the alternator on a bench tester and either it is the alternator or not. Most times it is the alternator. I am assuming that the Autozone alternator has an isolated ground stud. Not sure if it does. It will need to be isolated. But I am not a smart man when it comes to these problems. I know just enough to keep me on the road for many years. When I can't figure it out I phone a friend or go see Leidy's Repair in Lebanon PA. Good Luck.

Take the alternator back where you bought it and let them test it. If it is not working they should replace it.

I am not familiar with a popping battery, what is that?

Have you cleaned the 2 wire plug brown and red wire, that is on top rear side of the alternator? Corrosion, oil usually takes place here and the connection get weak. Some times I have to unplug and clean or just plug back in and light condition goes away.

cucvrus said:

I am assuming that the Autozone alternator has an isolated ground stud. Not sure if it does. It will need to be isolated.

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No drivers side does not need to be isolated only passenger...

Autozone... POS is likely bad

What is a popping from the battery you mean the thing exploded? Maybe someone can chime in on exactly what triggers that light... at 14.5 volts you should be fine... Oh and clean all your grounds XD

Matt5 said:

No drivers side does not need to be isolated only passenger...

Autozone... POS is likely bad

What is a popping from the battery you mean the thing exploded? Maybe someone can chime in on exactly what triggers that light... at 14.5 volts you should be fine... Oh and clean all your grounds XD

Click to expand...

My CUCV has the isolated ground on the DRIVERS SIDE alternator. But maybe the CUCV TM's will show different.

I hope my 1008A1 is not wired wrong. If it is the gremlins must have done it.

... really only the drivers on a stock setup? your wording makes it sound like it's driver side only as you did not say "both"

I'll go from here on out assuming you do not know how the electrical works in these trucks...

To condense on parts a stock cucv has 2 isolated ground alternators...
Does it need 2?
No
Driver side is 12 volts, 12 volts can ground to the body with no issues their for you can run either the stock isolated or non isolated ground
The passengers side is 24 volts... the positive of the drivers side connects to the negative of the passengers side...
Well... if you hooked +12 to ground... eh you might have some sparks to say the least...
So passenger, yes must be isolated... drivers however... matters not.

So the statement saying "it will need to be isolated" is completely wrong and has no effect on any of the ops problems. It can be if you want, I myself would keep both isolated as really what's the difference (but I also have a local re builder)

Passenger, yes 100% MUST be isolated or, the second you go to hook it up you will know something is not right... but again, drivers side no, it does not.

I am OK with being wrong. I just thought they put that isolated ground wire on the Gen 1 for a reason. To make both alternators interchangeable. It was there and worked for 35+ years so everytime I replace an alternater on the drivers side I make sure I put the ground wire back on. Stupid is as stupid does. I liked paint by numbers when I was a kid. It made the painting come out just like the picture on the box. If I substituted one color for another I ended up with a picture that was not a beautiful as the original. My point is it worked with the wire all that time. I put the same wire back on and it works. My goal has been met. I don't know why but I use books and experience to guide me thru repairs. Isn't that why everyone here references TM's when questions are asked?. Have a Great Day. I will be out cutting up a CUCV. One door closes and another opens.

What I mean by popping a battery is when you have an old battery, most likely with a bad cell, that overheats when you hook up a new alternator and pushes most of the water/acid out without swelling or exploding. The battery was old, so I honestly wasn't surprised.

I have cleaned the contacts on the red/brown connector going to the back of the alternator, and I checked their voltage as well. I have 12V on the red wire with the key off and 11.9V on the brown wire with the key on. I also checked the voltage at the heater fuse and it showed 12.1V. According to the helpful threads section, the only thing between the heater fuse and the connector on the alternator is the Gen 1 light and the cluster plug on the back of the fuse block.

Based on the recommendations here and the procedures in the helpful threads section, I've narrowed it down to being either the cluster plug, the light itself?, or the new alternator. Everything else checks out or has been done to resolve the issue.

I admittedly don't know how that cluster plug disconnects and am having trouble finding it in the TM, so if someone could point me in the right direction I would greatly appreciate it. I'm hoping that cleaning the contacts there would resolve the .2V drop between the fuse and the exciter wire. I'm not sure if 11.9V on the exciter wire would be enough to turn on that light, but it only has a dim glow and I'd like to try and test that out before returning the alternator.

Thanks for all the input so far.

Honest question cucvrus, are you okay? You go on long random rants all the time here... and this most recent one... even if the reason was to be interchangeable (kinda... again, it's so the military had to stock 1 part not 2 not really for a field repair) you do not *need* to have an isolated one as you stated... you then go into talking about putting the ground wire back on, then talking about paint by numbers that has less than nothing to do with the issue at hand.

This is simple, the drivers side can use isolated or not, it will not effect anything at all... it is was done purely to have 1 part stocked vs two... this has nothing to do with paint by numbers, things working for 35 years, or stuff not being as beautiful...

Everyone here references TM's because they don't want to assist... that's why we hear "this was already discussed look for the thread".

OP the biggest pain with the cluster is disconnecting the spedo once you do that you can pull it out further to remove the plug, it has tabs on each thin side IIRC.

No I'm NOT OK. Please continue. Every once in a while I like to listen to a professional. I do have to ask. Why did they bother even putting the ground wire there on Gen 1? I know you have an answer. I just don't care why. It is there it worked with it and I put it back on. Good enough. Now back to my paint by number set. Have a Happy Time. Lord Richard is off to the Mt Hope Shire for the weekend.

It was a honest question as to your well being...

How does a isolated ground alternator work with no ground wire to ground it? You understand a "normal" alternator grounds via the case as well as any ground wire. But the case is connected to ground... If you were to connect 12 volts to that ground wire (to get 24 volts) it would be a direct short to ground, so we need to isolate that ground to prevent a direct short... They need the ground wire on gen 1 because with out it... the alternator would not work... it would have no ground... we already went over why it is a isolated ground unit...

If you do not care why things works as they do, I would not tell people how to fix stuff... it requires a understanding of how things work... this is why according to you, the OP had to buy a new alternator... (no isolated ground) when infact... that is not the case at all...

Also if the new alternator has a ground stud, no one said not to put the wire back on... all that was said was... the DRIVERS unit does not need to be isolated ground...

Then why did General Motors put a wire on if it was NOT needed? Why not just let the stud open on the drivers side? I know enough to keep several CUCV's on the road. I don't know how or why about everything. I know how and why things need changed when they don't work. I just do the bull work and the dirty stuff. I let experienced people work on things that I don't care to know the in's and outs on. I must get back to my paint by numbers. Have Fun.

As I said, if you put a isolated ground alternator... and don't ground it (with the wire......) it is not going to work because it is not going to have a ground... you can't leave the stud alone... it is the only ground for the alternator on a normal cucvs systems to ground...

The OP put a non isolated ground alt... DRIVERS side... that is fine, he does not need to replace it with a isolated ground one... I mean it was kind of that easy of a comment...

Cucvs are paint by number... this was swapping some numbers looks good still IMO...

Not to disparage the op thread any more but matt why would the manufacturer isolate the ground on the drivers side if the truck did not need it? After all I would like to know if a standard alt. will work to charge the battery by just case grounding. Is that what you are implying?

Yes matt since op went with non isolated ground alt on the drivers side then the charging system has changed. Both alts are still 12 volt.

Drivers side must have isolated ground wire. TM 9-2320-289-34, Appendix E, figure E-9. Passenger side alternator isolated ground post is not used.

Thank You Curtisje

I would, will stay with how the manufacturer designed the charging system.

Curtisje said:

Drivers side must have isolated ground wire. TM 9-2320-289-34, Appendix E, figure E-9. Passenger side alternator isolated ground post is not used.

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Is this entire thread turning into a troll now? Honest question... the most simple of things (btw the OP even said he used a PN from THIS WEBSITE "I used the Duralast alternator listed in the wiki") has turned into a page of the same thing being repeated 20 times...

Last time I am going to say this... the OP is using (I assume this is from memory) a 76 amp alternator non isolated ground from a old caddy... this will work for the drivers side... as THE DRIVERS SIDE DOES NOT NEED TO BE ISOLATED...

Why would the manufacture isolate the ground on the drivers side if it did not need it...

AS I SAID... so the military had to stock ONE part not 2... this is the ONLY REASON.

The alternator (a non isolated ground one) will work with out a ground wire... the case is a ground as well... if it is provisioned for a ground wire, yes it should be used... you can never have too many grounds... yet again SIMPLE...

I have no idea where that TM is or that figure... yet again... the VERY WIKI ON THIS SITE STATS DRIVERS SIDE DOES NOT NEED TO BE ISOLATED...

Passenger side ground is not used?

LOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL Really? I mean really?

Do any of you even own a cucv?

Oh and no, the charging system has NOT changed...

Matt5 said:

Everyone here references TM's because they don't want to assist... that's why we hear "this was already discussed look for the thread".

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Everyone wants to help.
But doing one’s due diligence in researching the issue before posting should be automatic. (Not including emergency’s).
Some people are simply not willing to invest the time and will post a question without ever searching or reading anything.
Otherwise this forum would have 300+ Threads of “Why is my GEN1 light Inop.” for example.

The TM’s are there for a reason.
It includes troubleshooting instructions.
The Search function is there also. Admittedly not the best, but it works.
Reading the old threads also yields an incredible amount of information.

Very rarely will a CUCV have an issue that has not been discussed.

Yep okay... This is pointless now... you have someone giving wrong info saying "look at the TM" and you still feel it is a good idea for everyone to go to the TM's...

Also... I have no idea how to even find that info... not all of us know or have the patience to try to find stuff in massive books... like give a page number...

going on 3 pages... fighting incorrect info since post 2... and I get the flack LOL...

I read a old thread once... Wasted my money old dated info that was wrong...

I actually read quite a few threads with wrong info...