CUCV M1009, Gen 2 Light on...

[camerodad]

Gen 2 Alternator:

When You had your alternators rebuilt, their is an extra wire on nthe PASS Side Alternator , this is because it has an Isolated ground, Make sure that the alternator was rebuilt correctly with the isolated ground.

 

[doghead]

When You had your alternators rebuilt, their is an extra wire on nthe PASS Side Alternator , this is because it has an Isolated ground, Make sure that the alternator was rebuilt correctly with the isolated ground.

"extra"? The stock alternators on a cucv are identical.

 

[tcg528]

Doghead, what exactly is the isolated ground in the system? I take it from your response that it is not an internal alternator configuration? By the wiring diagram, it looks like a capacitor between the negative Gen 2 post and a ground, but since my M1009 came to me so screwed up, I can't verify this.

 

[Warthog]

The "isolated ground" on the stock alternators has been talked about so many times it makes my head spin.....

The alternators are DelcoRemy 27SI Type 100 12v alternators that where redesigned by GM to meet the Military requirements for a 24v world.

In very simple terms the only difference between a civilian alternator and the military version is the the internal electronics of the alternator (rectifier and voltage regulator) are attached to the case with fiber washers. This "ISOLATES" the components from the case.

Now how do you gound something that is "isolated", you install a ground stud.

Instead of using the case/housing to ground the circuit, you use the ground stud.

Thats it, Nothing else. Very simple.

To create the 24v, the GEN1 output is feed to the ground post on GEN2.

GEN2 is only producing 12v, but when it is combined with the output of GEN1, you have 24v.

The Capacitor/suppressor you see in the wiring diagrams are for noise suppression when Military Radios are installed. They where standard on all trucks because they wanted one item to stock as thet had many differnt versions of the CUCV. No need to stock 10 differnt versions of an alternator when one whould do.

If you don't have the radios, the capacitor is not required.

 

[tcg528]

Thanks Warthog. I've searched for it on here and Google, but nothing I found put it as simply as that. In order to convert an isolated ground into a case ground, all someone would have to do is remove that fiber washer? And to convert a cheap case ground alt into a $200 isolated ground alt is add a fiber washer?

 

[Warthog]

Thanks Warthog. I've searched for it on here and Google, but nothing I found put it as simply as that. In order to convert an isolated ground into a case ground, all someone would have to do is remove that fiber washer? And to convert a cheap case ground alt into a $200 isolated ground alt is add a fiber washer?

It is a little more complicated than that , but yes that is the basic idea.

My local alternator rebuilder has a couple of dozen old Cadillac alternator sitting on the shelf that he can convert to "isolated ground" units. It takes him 30 minutes or so. The hard part is finding the correct mounting bolts.

 

[1stSarge]

Isolated Ground...

 

[tcg528]

 

[hoplite666]

I was having issues with the gen 2 light flickering when coming to a stop and at idle. I turned up the idle screw and problem gone.

 

[Kevin majors]

i just got my two alternators back from the shop........and yet...my gen 2 light comes on.....as soon as i put lights on....or the heater blower fan on.......kinda weird that the light would come on......even while im driving...it comes on........what am i overlooking?

thanks mario

Mine dose that to how did you fix it

 

[Utah CUCV]

Only 24 volt stuff runs off bat 1 and bat 2 in series, which on the CUCVs will only be the glow plugs (which have a resistor to reduce 24 volts to 12 volts...but that doesn't really matter for this situation), starter, and blackout lights (and military radios, the NATO slave cable, and some other "accessories", which I'm assuming you don't have). Those shouldn't be drawing any power except when you are starting the engine or when you are running the black outs. So I would suspect the bat 2 isn't holding a good charge, so it is overtasking the gen 2 circuit and causing the light to come on. In fact, whenever a gen goes bad the bat is usually soon to follow, and vice versa. This is because when one goes bad it puts an increased strain on the other.

Because of the grounded gen 1 circuit which has a battery in series with the isolated gen 2 circuit battery, it will cause battery testers to give bogus readings. I recommend disconnecting each battery from the truck before trying to connect a tester. If the battery is good, I would check all the wiring on the isolated circuit to make sure connections are good, nothing is corroded, and nothing is grounding to the vehicle body or something like that. The gen 2 circuit is supposed to be completely electrically isolated. The only time electricity is used from the gen 2 circuit is when bat 1 and bat 2 are used in series to create 24 volts.

Both bats need to be whompers as far as cranking amps. If you have some wussy regular car batter, that might also be the problem.

So the NATO slave cable socket is connected to the two batteries in series. And sometimes there are other power cables (for radios and other accessories which are probably not on your truck) which are also connected to the two batteries in series. It might be worth it to disconnect those kinds of things, just in case they are allowing a small amount of electricity to ground to the vehicle body. These would not be in full short, or there would be serious problems. But on a 30 year old truck, it is always possible electricity is bleeding through worn insulation or corroded connectors or something like that.


Good luck.

Utah CUCV