GEN 2 Light is on (but dim) AND VoltMeter doesn't work???

[CCATLETT1984]

no troubleshooting for the wiring, if the alternators both test good, then a test light and a multimeter will become your friends.

just have them test each one as a normal 12v alternator, they will need to hook the negative of the machine up to the ground lug on the alternator, but if they dont know that then i would go to another shop.

 

[MuddWeiser]

ALSO:

" First step is to put your voltmeter on the output of each alt and see if there is about 15 volts there running..."

Im confused - so I can check this myself while the vehicle is running? If I were to put my voltmeter on the "output" - where do I ground the voltmeter??? Im still trying to figure out this "isolated ground". Does that just mean that there is an actual ground wire going to each alternator - and the alternator is not grounded through its housing?I.E. the ground stud on the alternator is isolated from the case?

Im nervous to start poking around because other threads I have read here while searching talk about accidently frying the alternator by grounding to the wrong spot...

 

[mangus580]

Im still trying to figure out this "isolated ground". Does that just mean that there is an actual ground wire going to each alternator - and the alternator is not grounded through its housing?I.E. the ground stud on the alternator is isolated from the case?

You got it. Instead of grounding through the case, they put a specific ground stud on the back. The reason for this, is to wire 2 alternators in series in order to produce the 24v.

Something you might look at, is there is a small push on terminal on the back of the alternators. Make sure it has a good connection (as well as the rest of the wires). Also, replace the offending bulb with another one. Make sure someone didnt replace it with say a 24v bulb? Sure would make it dim!

 

[Michael]

5.1. GENERATOR LIGHT DOES NOT COME ON WITH KEY IN “ON” POSITION BEFORE ENGINE IS
STARTED (ALL MODELS EXCEPT M1010)
Step 1. Trace all circits from generator to generator light in instrument panel (including
fuse, bulb, arm relay}. (See wiring diagram F-11)
If circuits are good, replace alternator. (See paragraph 4-2)
6. GENERATOR LIGHT REMAINS ON OR TURNS ON DURING OPERATION (ALL EXCEPT M1010)
Step 1. Check engine idle speed. (See paragraph 3-25)
Step 2. Disconnect connector from left alternator (if “GEN 1“ light is on) or right alternator (if
“GEN 2“ light is on). Turn key to “RUN” position.
If generator light is not on, trace circuit from alternator connector to generator
Iight in instrument panel. (See wiring diagram F-11) If circuit is good, replace
alternator. (See paragraph 4-2)
If generator light is on, trace circuit from alternator connector to generator light
if instrument panel. (See wiring diagram F-9)
Change 2 2-59
TM 9-2320-289-20
Table 2-4. Electrical Troubleshooting (Con’t)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
7.
8.
9.
10.
“GEN 2“ LIGHT REMAINS ON WITH KEY IN “OFF” POSITION (ALL EXCEPT M1010)
Step 1. Remove generator 2 relay. (See paragraph 4-9)
If light goes out, replace relay.
If light remains on, trace circuit through brown/red lead to “GEN 2“ light in
instrument panel. (See wiring diagram F-9)

This is what I was referring to. page 108 of the -20. I don't know if it has anything to do with your problem.

I test mine across the pos and neg post of each battery with a good digital volt meter. You should get better than 14 volts but less than 15. 14.3 to 14.5 is best. A fully charged battery will have 12.5 volts unless it has just been removed from the charger and hasn't had a load put on it, in which case it will read higher with a digital volt meter. You can either hit the starter or turn the lights on for a few seconds to remove this "float charge". 26.72 volts tells me one alt is working and one isn't if I was a betting man.

There is suppose to be something you can do at the alternator to trick it into putting out full power but I can't remember what it is. I think it is to remove the two wire connector and jump the two spades but I wouldn't do it unless someone confirms that this is correct.

 

[MuddWeiser]

THANK YOU SO MUCH!!!! That is exactly what I was looking for!

I was looking in the "alternator section" of -34 and -20 and wasn't seeing anything but how to remove, dissasemble and test the alternators!!!!

Pointing me to the 2 wire plastic plug at the alternator was a huge help!

WHAT I FOUND:

I unplugged the 2 wire connector at the suspected bad alternator (the one with the dim light) and the light did NOT come on in the " Key ON" position. After looking over the diagram, a buddy then mentioned that I jump the brown wire on said plug to the ground terminal of the battery that goes to "chassis ground" . VOILA - LIGHT TURNED ON BRIGHT (eliminating my suspection that the printed circuit board or wiring to the light was bad).

I am leaning towards a bad #2 alternator BUT before I replace it --- he wanted me to ask if anyone knows what the #2 field current relay does? On the schematics, this is listed on the extreme right side of the page (about half way down) and points you to figure E4 (in the appendix of -34) for continuation of the circuit??? He seemed to think that could also cause the problem but said it was MOST PROBABLY a bad alternator???

Any way to test this #2 Field Current Relay?

As stupid as it sounds I was happy to see the light turn bright during his test, as I would rather spend the $$$ to get the alternator replaced then hunt down a wiring issue... I just find it easier to unbolt and replace the alternator vs. hunting and replacing wiring!!!

Thanks again for pointing me in the right direction and helping me diagnose this problem.

WHERE IS THE BEST PLACE TO BUY A REPLACEMENT ALTERNATOR? I DON'T TRUST MY LOCAL ALTERNATOR SHOP TO REBUILD IT...

 

[acetomatoco]

My gen 2 light was dim and the second alternator relay would not kick in until I took out the little bulb holders and cleaned the green goo off the contacts with a jack knife and put in new 168 bulbs and used dieelectric grease on the whole mess... Green corrosion acts as a poor ground... pull out your two bosch relays and shine up the blades on them and shove em back in good....The leaky windshields and the mice peeing behind the dash when they are living on the desfoster ducts tend to corrode everything in the CUCV..and smell poorly too...shop vacuum and 409 help some...

 

[acetomatoco]

The stud with the ground strap is the isolated ground.. it does not ground thru the case of the alternator The other isolated ground on the right hand alternator is how they get them in series...just like the batteries... one ground on the front battery is the circuit ground and the second ground on the rear battery is connected to the positive terminal on the front battery... just like in a flashllight.

 

[Michael]

You might want to read this thread before you buy a new alternator.

http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=12291&highlight=alternator

Interesting reading on GM alternators:

http://www.madelectrical.com/electricaltech/delcoremy.shtml
but remember CUCV's have a 27si

http://www.madelectrical.com/electricaltech/remotevoltagesensing.shtml

http://www.rowand.net/Shop/Tech/AlternatorConversions.htm

 

[ultim8gamr]

I ran into this problem running up north this weekend. On the drive up it was raining and the gen 2 light would come on every now and then after the first 100 miles of driving. then after arriving at my destination ( only 200 or so miles) i realized that the gen 2 light stays on all the time just very dim. it doesnt go on bright upon startup like it used to either. So is the consensus that this problem generally comes from the wiring or within the alternator? I just bought the pass side alt 6 months ago so it shouldnt be going out so soon.

 

[Armada]

I had my alternators professionally rebuilt from a reputable starter/alternator shop. I ran the truck a few times and they worked great. About a week later I went out to the garage and the #2 gen light was dimly glowing and the key wasn't even in the ignition. It stay on when the engine was running also. I pulled the alternator out and took it back to the shop for testing. Something had shorted in it (I forget what). He wanted to know if I had reversed the polarity at all, and I hadn't. He said that type of failure is rare but can happen. Poor quality foriegn part I'm guessing. They repaired it and it has been fine ever since.