Cucv alternator problem

[Laszlo]

On an 84 cucv pickup. On the isolated ground alternator. What two signals enter the alternator via the two blade plug? I have 24v on one side. And I cant figure out what the other side is? Which is the exiter input? And what voltage should it be. I have no responce from my gen 2 light. Although IV verified the bulb and holder and the printed circut board. The light used to work but now nothing. Also my volt guage isnt working. Did the 300 ohm resistor replacement. It just does nothing. I do have 24 volts at meter harness. All this is cause I'm tracing down low voltage output from gen 2. 12.9 is all I'm getting. 14.2 on gen 1. Bit I think its just Bleeding thru from gen 1 being wired hard in series. Like theyre equalizing. Its driving me crazy. IV tried everything and been thru the whole system. In missing something. What is the gen 2 light signal coming from at start up.any help would be appreciated. Ty

 

[Barrman]

I have to ask. Have you followed the steps in the -20 TM for diagnosing electrical problems? That is really the bible for these vehicles and is right on. Start where it starts with two fully charged and load tested batteries. Then, follow the steps in the -20.

There is a tool called a Power Probe 3. Kind of pricey, but get the Power Probe 3 master kit for around $300 on Amazon. It is a volt meter, test light and much more. It makes doing alternator and wiring checks so much easier in my experience. One of my M1009's last week fired up with the Alt 1 light glowing. I keep a rebuilt alternator on the shelf just for this reason. I didn't check anything or do any test. I just swapped them out. Fired it back up and the light is still on. Then, I got the Power Probe out to do what I should have done 10 minutes earlier. No voltage at the stud on the back of the alternator. I traced the wire to find the fuse able link at the firewall bus bar had broken. (Probably from a cat or 3 playing around under the hood is my guess.) A regular volt/ohm meter works too.

 

[Laszlo]

IV been checking the output daily at startups . I adjusted the belt the other day cause I noticed a little slipping occuring. and out of no where. 14.5v. I am wondering whats the voltage cut off limit set to. For instance if I had 12.9 does it tell the regulator to turn off or "idle" . or was my belt slipping worse than I thought. Im sure it was turning when I tested it and got 12.9v.
I dont know. also IV heard of SI tyoe alternators loosing magnetism after a time. And needing to be " jump started" or excited? Not sure if that was the case or not. I need to print the manuals cause scrolling thru it on my phone is like torture. But I intend on reading up on everything about this truck. Thanks for everyones help.

 

[Tow4]

IV been checking the output daily at startups . I adjusted the belt the other day cause I noticed a little slipping occuring. and out of no where. 14.5v. I am wondering whats the voltage cut off limit set to. For instance if I had 12.9 does it tell the regulator to turn off or "idle" . or was my belt slipping worse than I thought. Im sure it was turning when I tested it and got 12.9v.
I dont know. also IV heard of SI tyoe alternators loosing magnetism after a time. And needing to be " jump started" or excited? Not sure if that was the case or not. I need to print the manuals cause scrolling thru it on my phone is like torture. But I intend on reading up on everything about this truck. Thanks for everyones help.

These alternators don't loose magnetism as there are no magnets like in a generator. The regulator set point is 14.8 volts. You should see a tenth of a volt one way or the other depending on the battery state of charge.

 

[Laszlo]

These alternators don't loose magnetism as there are no magnets like in a generator. The regulator set point is 14.8 volts. You should see a tenth of a volt one way or the other depending on the battery state of charge.

On rare occasions, the alternator can become demagnetized when it’s been on the shelf for a prolonged period of time. When that happens, the voltmeter indicates battery voltage instead of the typical alternator charging voltage.

Before you remove the alternator, first try to determine if a loss of residual magnetism is causing the loss of voltage. You can do this by flashing the field:

1. With the vehicle ignition in the “off ” position, remove the rubber boot from the alternator battery terminal and the rubber grommet from the small “R” terminal.
2. Take a small piece of wire and touch one end of it to the battery alternator terminal. Then touch the other end to the small "R" terminal. (Note: This may create a small spark, which is normal.)
3. Remove the wire and start the vehicle. The voltmeter should now increase its voltage reading to around 14 volts.
4. If the alternator isn’t charging, then re-check all connections and belt tension before removing the alternator.
5. Put the rubber boot and the rubber grommet back on.