Gen 2 / Front battery issue

[Timber01]

I did search & found some similar problems but no direct solutions. We have 2 1985 M1008's as brush trucks. The 1 has this problem. Both Gen lights come on with ignition. After starting the Gen 2 light stays on but goes off with a tap of the throttle. The charging meter will cycle back & forth between low green & mid yellow after starting and after a day or 2 stay in the yellow & slowly drop. The front battery goes dead after a few days of driving and quicker if using lights. Voltage across the front battery & LH alternator is 12.4V while idling. Voltage across RH alternator & rear battery is 14.7V. Replaced both batteries and LH alternator. Nothing changed. Somehow the front battery is not charging, and the output from the LH alternator is too low. I plan on doing an alternator swap with the other truck to see if maybe the shop just cleaned it instead of re-building it, but what exactly should I be looking for to cure this?
Thank you,
TM
KCFD6

 

[gaunt1969]

My 1028 was doing the same . It was the LH Alternator. If its not putting out 14 to 14.7 it is bad. Mine the strap inside the alt from the diodes to the pos post was corroded and loose, was only getting about 12.8 v out of it, just enough to keep the light from comeing on, but way to low and not enough current to do any good.
Also this can cause your gp relay to chatter after the eng is running. As long as the back one is chargeing it will still crank without little trble. "untill it gets cold" * Drove me nuts for a few hrs till I figured it out*

 

[doghead]

Test each batteries voltage before, and after starting the engine. If there is no increase in voltage while it's running, you have an alternator problem(most likely).

 

[Timber01]

Thanks. That is what I'm suspecting. After I swap the alternators tonight it will confirm it is the alternator. Then it's back for warranty repair. I hope that is it & not some wiring nightmare!

 

[Timber01]

Well the alternator was the problem. Swapped it out & everything works like it should. The new alternator goes back to the shop