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

[MuddWeiser]

So I fired up my CUCV and the GEN 2 Light is on; but is very dim (compared to GEN1 light before cranking up).

The voltmeter is also not registering anything (stays all the way to the left "BATT").

Does this mean the passenger alternator is dead???

Can I just go to NAPA and buy a replacement alternator or is it more complicated that that?

I have the Delco alternators...

Thanks in advance...

 

[devilman96]

RE: GEN 2 Light is on (but dim) AND VoltMeter doesn

Ya need to get out your TM and meter for some troubleshooting...

Napa alternators will not work, CUCV's have isolated grounds.. You can have this done at a local shop (usually)... If not I have them here.. http://odiron.com/store/index.php?cPath=17_39

 

[MuddWeiser]

Well if I am going to replace one, I might as well replace them BOTH. Can you help me out a little before I decide to buy 2 new alternators? I am new to the whole 24v system... It is my understanding that both alternators are 12v. But I don't know how or where all their wires work/go?

What should I do first? I have the cartoon "troubleshooting a charge" service procedure from this site - but it doesn't really help as all the steps check out... Belts are tight, lights turn on - I get 12.6v at each battery while truck is running etc... But the GEN2 light stays lit and is dim. Headlights are Dim and the batteries die after about 15-30 starts AND THE VOLTMETER ISN'T REGISTERING ANYTHING - It has always stayed at "BATT" in the red, never moves.

I wasn't able to locate the following items referenced in the guide though:
Where is the passengers side #2 Field Current Relay? What about the fusible link???

I don't have a TM? I do have a voltmeter? Can you give me some step by step help to figure out if it is a wiring issue or if the actual alternator is dead?

If it helps, with the key on (ignition OFF) - all my lights come on (Oil, Gen1 and Gen2). The Gen1 light is BRIGHT and the Gen2 light is not as bright (they both have new GE 168 bulbs). Once I crank and start the motor, Gen1 and Oil light turn off, Gen2 light stays lit but still dim.

Thanks again - I love this rig and want to get it reliable before the snow starts to fall this winter!!!

 

[acetomatoco]

Spend the $ and get the manuals... the -20 and -34 have page after page of schematics and troubleshooting advice. First step is to put your voltmeter on the output of each alt and see if there is about 15 volts there running...

 

[devilman96]

Ya need to put away the catroons and go here... http://www.steelsoldiers.com/index.php?module=pagesetter&tid=1 Down load the CUCV TM's and read through them all... It will take you step by step by step through trouble shooting the charging system on the truck and or anything else you may have trouble with.

If you have a gen one light going off you have at least one good alternator... No need in buying two of them or any for that matter... Not untill your sure thats what is going on.

 

[CCATLETT1984]

both alternators are the standard GM large frame 100amp alts, with the exception that they have a ground stud that is Isolated from the case. any alt/starter shop can rebuild them, should cost around $100 ea.

There is actually a civilian part# that comes with the isolated ground, but i dont have the number with me.

 

[MuddWeiser]

Thanks

Thanks for the heads up --- I didn't know the ACTUAL TM were available here...

I am however, having trouble finding the proper TM (the -20 and -34) you referenced above?

Do you have the complete # ? i.e. "TM 9-2320-289-20P"

Also is there a way to SEARCH the TM's by #???

Or if someone could just provide a link to the actual manual I would appreciate it...

Sorry if I seem helpless im not to good when it comes to websites...

 

[GM72K10]

RE: Thanks

click on TM 9-2320-289-20 in the technical manuals, etc,TM 9-2320-289-20P, TM 9-2320-289-34, TM 9-2320-289-34P

 

[CCATLETT1984]

RE: Thanks

also both your alternators should be putting out about 14v at the batteries when running, yours are not putting out. its prolly a burned out diode inside the alternator, any alternator/starter shop can test it and rebuild for ya.
I know the TM section of the site is a pain, In my spare time (not much lately) I've been trying to come up with a better layout thats easier to navigate.

 

[MuddWeiser]

20P has an issue - says file is corrupt?

20P has an issue here on this server - can I get it somewhere else?

So I got 34, 34p and 20.

I was looking in 34 and there is an alternator TEST section. But it requires special tools? What do you guys do about that???

Is there a better section in one of the other manuals???

 

[CCATLETT1984]

RE: 20P has an issue - says file is corrupt?

to test them just pull them and take them up to the local parts store to test.

 

[MuddWeiser]

So during my troubleshooting I noticed the flimsy circuit board on the back of the guage panel MAY be the problem??? I need some advice:

I pulled the bulb out of the GEN2 idiot light. I replaced it with a NEW GE168 bulb. When I went to put it back in, the light did not come on during "pre-ignition"(key on, engine off). The Gen 1 bulb still came on so - I pulled Gen2 bulb again and shined a flashlight up behind the dash and it almost looks like the copper contacts on the printed circuit board MAY be damaged (that flimsy piece of plastic with copper circuits running through it - fixed to the back of guage panel). I put the bulb back in and the Gen2 light came back on BUT IS STILL VERY DIM (compared to Gen1 idiot light). THEY BOTH HAVE NEW BULBS.

Are the bulbs supposed to be bright ALL THE TIME? It seems to me, if the vehicle is not running (key on, engine off) the bulbs should both be on AND THE SAME BRIGHTNESS?

If the alternator is bad, and the engine isn't running - would the light be dim, OR should it always be the same brightness. If thats the case, since my Gen2 bulb is dim (compared to the Gen1 bulb) does this indicate a bad contact to the flimsy circuit board on back of guage panel???

Thanks again - still trying to figure this out?

 

[ida34]

With all this work you have been doing I would just take the alts off and have them bench tested. Who ever you have test it make sure they know what the isolated ground is. If they do not know what your are talking about then take it to another place to test. If they hook it up like any other non-isolated gm alt sparks will fly.

 

[MuddWeiser]

Taking the alternators off is my next step. But right now I am curious as to why the light would be dim prior to starting/cranking the engine? I thought the light was supposed to come on bright on "key on, engine off" prior to startup - to show you that the bulb is good. Gen1 idiot light is bright and Gen2 idiot light is dim. Would a faulty Gen2 alternator cause the light to be dim on pre-ignition (key on, engine off)?

 

[Michael]

The light could be dim because of a problem in the alternator or the wiring between the bulb and the alternator. There is a step in the troubleshooting section that covers this. I have had a lot of problems with corrosion in the dash myself.

You need to go through the -20 troubleshooting and then do the -34 if you haven't fixed the problem. That is the way the military designed it. The lower levels check the simple stuff and if they can't fix it pass it on to a higher level of maintenance. You can also download the manuals from the government site. Put M1008 in the pub title text box. You can only download TM that are for public release. If they ask for a password the TM is restricted.

https://www.logsa.army.mil/etms/ind...f8d006c14-AF82DDF1-0AD1-C4FC-F4111696E0DC321F

 

[MuddWeiser]

I had the alternators tested and they put out 26.72v total? Is this normal good voltage? Does that mean that BOTH of my alternators are good? I don't know if the shop tested them properly as they didn't have me remove them because they said that wasn't necessary . They ended up putting a voltmeter on ALT2 (passenger side) positive feed, and then grounded the other end. The meter read 26.72v and they said that means both alternators are working. They said most probably the problem is in my wiring.

What and where should I begin to look now??? It seems to me that even if the alternator was bad, the light should still be BRIGHT on (key on, eng off)... Please correct me if I am wrong as I really have no clue when it comes to a 24v system???

 

[CCATLETT1984]

thats low, should be 14v each, total should be around 28v

 

[MuddWeiser]

Am I missing something here? I keep referring to these service manuals referenced above and I don't see anything that has to do with trouble shooting the electrical WIRING? I.E. I am looking in -20, ch 4, where it shows the removal and replacement of the alternators and how to check belt tension... and -34, ch 4-2, is alternator testing and repair.

Can someone chime in with where I would find the electrical system diagrams or how to hunt for bad wires/relays etc...

Thanks, I am pretty much at a standstill here...

 

[CCATLETT1984]

the full diagrams are in the appendix section of the -34, appendix E if i remember correctly.
there are no relays in between the light in the dash and the alternators. the lights are there to provide a slight draw on the alternators to "excite" them into producing voltage. the civilian trucks simply have a resistor on the wire instead of the lights.

you really should have your alternators tested out of the truck, each should put out ~14v testing them together can hide some issues since one alt might be overvolting while the other could be undervolting.

 

[MuddWeiser]

thanks for the heads up on the wiring in the appendix.

is there an actual "troubleshooting" section that deals with the wiring? Maybe a step by step check this then this etc...


Okay I want to pull the alternators and take them back to the shop. They have a bench test unit but didn't know to test a isolated ground alternator. In fact they were telling me it is NOT an isolated alternator because the driver side has a ground strap that runs to the block (the passenger side does not) Can someone explain how to bench test an isolated ground alternotor - I.E. how can I make sure they hook these up right at the shop - or is a special "testing unit" required???