Gen 2 issues

First, let me say that I know the wiring in this truck is exceptionally jacked up. I want to figure out this Gen 2 problem and then I'm going to re wire it properly.

Now for the Gen 2 issue. I bought the truck (M1009) last August and have had intermittent battery problems. Finally it dawned on my that Gen 2 was the likely culprit because it was always the back battery giving me issues. I had it tested and then rebuilt about a week ago, put it in the truck, and still batt 2 wont charge. I thought the alternator may have been a dud so I took it out and had it tested again, but it works fine.

Now comes the wiring, which is horrifying to say the least. I believe it is all hooked up more or less "right" now, but here it goes.

Batt 1 neg to 24v neg buss bar, the small bottom one. Its not hooked to the larger 24v pos buss bar, it's grounded to the engine
Batt 1 pos to batt 2 neg, the small 12v eng wrg harness block on the right through the batt 2 neg post (which is hooked to batt 1 pos so it's basically the same thing) and gen 1 pos
Batt 2 neg to batt 1 pos, alt 2 neg, and eng wrg harness block (yes, some of this explanation is redundant)
Batt 2 pos to 24v buss bar (which serves as both pos and neg) and alt 2 pos through the 24v buss bar

Alt 1 small pos to eng wrg harness block
Alt 1 exciter to dash gen 1 light
Alt 1 pos to batt 1 pos
Alt 1 ground to engine
Alt 2 small pos to 24v buss bar
Alt 2 exciter to alt 1 exciter via jumper cable (gen 2 light socket is messed up and doesn't work. A job for another day.)
Alt 2 pos to batt 2 pos through 24v buss bar
Alt 2 ground to batt 2 neg

Batt 1 reads 14v and some change when running
Batt 2 reads 12v and some change when running

I can't seem to figure out why alt 2 wont charge the rear battery. Any help would be greatly appreciated.
Thanks

MtNgranek said:

First, let me say that I know the wiring in this truck is exceptionally jacked up. I want to figure out this Gen 2 problem and then I'm going to re wire it properly.

Now for the Gen 2 issue. I bought the truck (M1009) last August and have had intermittent battery problems. Finally it dawned on my that Gen 2 was the likely culprit because it was always the back battery giving me issues. I had it tested and then rebuilt about a week ago, put it in the truck, and still batt 2 wont charge. I thought the alternator may have been a dud so I took it out and had it tested again, but it works fine.

Now comes the wiring, which is horrifying to say the least. I believe it is all hooked up more or less "right" now, but here it goes.

Batt 1 neg to 24v neg buss bar, the small bottom one. Its not hooked to the larger 24v pos buss bar, it's grounded to the engine
Batt 1 pos to batt 2 neg, the small 12v eng wrg harness block on the right through the batt 2 neg post (which is hooked to batt 1 pos so it's basically the same thing) and gen 1 pos
Batt 2 neg to batt 1 pos, alt 2 neg, and eng wrg harness block (yes, some of this explanation is redundant)
Batt 2 pos to 24v buss bar (which serves as both pos and neg) and alt 2 pos through the 24v buss bar

Alt 1 small pos to eng wrg harness block
Alt 1 exciter to dash gen 1 light
Alt 1 pos to batt 1 pos
Alt 1 ground to engine
Alt 2 small pos to 24v buss bar
Alt 2 exciter to alt 1 exciter via jumper cable (gen 2 light socket is messed up and doesn't work. A job for another day.)
Alt 2 pos to batt 2 pos through 24v buss bar
Alt 2 ground to batt 2 neg

Batt 1 reads 14v and some change when running
Batt 2 reads 12v and some change when running

I can't seem to figure out why alt 2 wont charge the rear battery. Any help would be greatly appreciated.
Thanks

Click to expand...

Far from an expert on CUCV electrical, the highlighted points do not make sense to me. Not that it means much.
But without an operational Gen 2 light, I wouldn't expect that alternator to work.

MtNgranek said:

Alt 2 exciter to alt 1 exciter via jumper cable (gen 2 light socket is messed up and doesn't work. A job for another day.)

Click to expand...

Fix this. The resistance of the light bulb is part of the circuit. Massively stupid, but that's the way GM made it.

Bingo MarcusOReallyus. Love GM but sometimes . . .

I figured I'd revive this thread instead of creating a new one.
I'm now having issues with Gen 1. I noticed the other day that the volt meter was showing lower than normal, and
Gen 2 is newly rebuilt(since April), so I figured it was Gen 1. Popped the hood and it was filthy and covered in black dust.
Took it to Autozone(mistake), and then to the Alternator repair shop to be rebuilt. Got it back, put it on, and it's acting
weird.
The Gen 1 light comes on before start, and goes off after start..
The exciter wire is getting 0v with key off, 12v with key on.
The battery shows 12.9v truck off but only 13.3v truck on. Alt shows 13.5v truck on.

Gen 2 shows normal 14.9v truck on.

I can't seem to figure out why Gen 1 only seems to charge at 13v instead of 14.9v.
I'm not even sure if Gen 1 is charging at all, at that voltage.

Any help would be greatly appreciated. Getting cold here in Chicago, and I need to put the Camaro back in the Garage.

Maybe the alternator shop put in the wrong regulator.

Measure battery voltage without running, and with running to see what your alternator output is.

Front battery voltage, and rear voltage. Don't measure in series.

Truck Off
Front 12.0v
Rear 12.8v

Truck On
Front 12.6v
Rear 14.8v

I measured the Gen 1 Output as well 13.0v

I don't understand how you get 13.0v output on gen one when you posted the front battery voltage running is 12.6.

From your numbers, it looks like alt 1, (drivers side), front battery, is not charging.

I don't understand why I'm getting two different voltages either. I figured Alt 1 still wasn't charging, but I wasn't sure, as the voltage does jump, just not much.
I figure it's the alt because the Gen 1 light is working and I'm getting exciter voltage. Just wanted another opinion from people who know more about this than I
do before I go back to the Alt shop and ask whats going on.


Thanks for the help thus far.

You should put a charger on that front battery. 12.0 volts is considered a dead battery if all the cells in it are good. I wonder if you just don't have a dead cell in the front battery pulling the voltage of the alternator down. I've seen it happen to cars that come to our shop, and the alternator will have an output of 13.0 or so running. With a good battery, it goes up to 14.4.

Could the wrong regulator have been installed when it was rebuilt?

Charge the front battery and then swap the front battery to rear, rear battery to front and see if the problem moves. As noted above, 12 volts is a dead battery. You should see 12.7 volts fully charged.

I finally got around to messing with this. The following has been done so far

I hooked everything up properly, but gen 1 does not charge. Gen 2 charges fine.
I took the truck to the auto part store to test the battery. They said it was low, but tested good.
Took the alt back to the place that rebuilt it and had them retest it. They tested it in front of me and it was putting out 14v.
I tested all the connections with key on and off, including the exciter wire. Everything is getting proper voltage. ie:12v on 12v wire constant and 12v on exciter key only.
I even cleaned the alt plug to eliminate resistance as a possible culprit. The plug was so filthy it was a possibility.
On the off chance the plug was bad in some other hitherto unknown way, I unplugged it, ran a jumper from 12v constant to battery, and a jumper with a light bulb from exciter to windshield washer fuse (keyed only fuse).
Lastly, I switched the batteries around.

As of now, none of this has worked.

One other symptom:

When I turn the key to accessory the gen 1 and gen 2 lights illuminate. When I turn the key to start the gen 1 light goes off but gen 2 stays lit until the truck starts.

This from the original Gen 1 post is still accurate:

The Gen 1 light comes on before start, and goes off after start..
The exciter wire is getting 0v with key off, 12v with key on.
The battery shows 12.9v truck off but only 13.3v truck on. Alt shows 13.5v truck on.

Gen 2 shows normal 14.9v truck on.

Any new ideas would be greatly appreciated.
Thanks

That gen 2 light staying on--that's normal so long as it shuts off within a few moments after the vehicle is started.

I wonder if you have a partially burned fusible link. Corrosion on the instrument panel PCB?

I had a gen 2 gremlin and the only way I found the trouble, was by getting intimate with the wiring diagrams and following the circuits forward and backward, checking EVERYTHING. Yup, it Sucks, but, get out your meter and diagrams, stick with it, and you'll find it...

Does your heater blower work? What is condition of fuse and fuse holder that blower circuit is on? This is same circuit as gen 1 exciter lamp, a bad fuse contact, or shorted blower resistor can cause problems with charging circuit.

You can test each alternator on the truck. The regulator terminals are terminal #1 (closest to B+), light (exciter) and terminal #2, battery sense. Terminal #2 is connected to the battery all the time. Terminal #1 is switched through the ignition switch.

Simply remove the regulator plug and run a jumper from the B+ alternator terminal to terminals #1 and #2. You can use a 10 ohm resistor instead of the light bulb in the #1 regulator terminal circuit if you like.

Doing this will take all of the truck wiring out of the equation (except the B+ and B- output terminals) and make it possible to determine if the problem is in the alternator or truck wiring. Measure the voltage at the alternator output terminals and at the battery posts. They should be within about .1 volt.

MtNgranek said:

I finally got around to messing with this. The following has been done so far

I hooked everything up properly, but gen 1 does not charge. Gen 2 charges fine.
I took the truck to the auto part store to test the battery. They said it was low, but tested good.
Took the alt back to the place that rebuilt it and had them retest it. They tested it in front of me and it was putting out 14v.
I tested all the connections with key on and off, including the exciter wire. Everything is getting proper voltage. ie:12v on 12v wire constant and 12v on exciter key only.
I even cleaned the alt plug to eliminate resistance as a possible culprit. The plug was so filthy it was a possibility.
On the off chance the plug was bad in some other hitherto unknown way, I unplugged it, ran a jumper from 12v constant to battery, and a jumper with a light bulb from exciter to windshield washer fuse (keyed only fuse).
Lastly, I switched the batteries around.

As of now, none of this has worked.

One other symptom:

When I turn the key to accessory the gen 1 and gen 2 lights illuminate. When I turn the key to start the gen 1 light goes off but gen 2 stays lit until the truck starts.

This from the original Gen 1 post is still accurate:

The Gen 1 light comes on before start, and goes off after start..
The exciter wire is getting 0v with key off, 12v with key on.
The battery shows 12.9v truck off but only 13.3v truck on. Alt shows 13.5v truck on.

Gen 2 shows normal 14.9v truck on.

Any new ideas would be greatly appreciated.
Thanks

Click to expand...

Do you have a ground wire from the alternator case stud to the engine/intake. That is an isolated ground alternator. I just glanced quickly at the post. If you covered that disregard my advise. Thank you. Happy Holidays.

I finally figured out what it was this afternoon. I took Tow4's advice and tested the alt on the truck and it was still running low.
Now I feel like an idiot because it turns out the belt was very loose. Apparently when I had the belts changed earlier in the year
the shop used the wrong belt. Should have known something was wrong when there was no more room to adjust the alt to tighten
the belt.
Thanks for all the suggestions.

HA!

Belts are very easy to replace yourself.

Now you know why most guys here do the work themselves.