M1009 Alternator/Charging Issue

[ADKM1009]

I have an 86 M1009. Have been fixing and tweaking stuff over the years and it has typically been rock solid but lately I have developed a tough to diagnose charging problem. The vehicle has the Roscommon 12V conversion. The Gen2 light used to come on right after I started it and once you revved the engine it would go out. Someone in the army had installed a voltmeter and it was pretty much pegged to the high end all the time. All of a sudden, after driving around for part of a day, stopping and starting the vehicle the batteries started to die down and then went kaput. Charged the batteries but had the same issue.

My first move was to take the driver's side alternator, which I still had, and put it on the passenger side. The original passenger side alternator felt like it had sand in the bearings. It went in for a rebuild. Unfortunately I am having the same issue with the driver side alternator now. The vehicle is a few hours from me and gets driven intermittently, but a few weeks ago I jumped in and it cranked and started instantly after having sat for a few weeks, and I mean instantly. Drove around town to run some errands and after the third stop and start the batteries were completely wiped out. The Gen2 light never comes on now, even just when you turn the key on.

I dug around on the site and research led me to believe it is the Gen2 dummy light. I have 8V across the bulb socket. Bulb is fine - it was a 168 so I replaced it with a correct, new 194. I have 12.55V of the back of the positive of the alternator with my multimeter grounded to the vehicle. I have 12.55v across both batteries when running. Shouldn't I have closer to 13.8V?

Because I am not around the vehicle every day, and where it is there aren't a lot of auto supply places, I tend to figure out what I might need and order up some supplies for the next weekend trip. I am thinking maybe I should replace all the fusible links?

Any other ideas or troubleshooting tips?

Thanks in advance folks.

 

[richingalveston]

I would start with the battery. If it has a bad cell, it will drain the other and drag your voltage down. check your fusable links with meter. replace what is needed, don't have to fix what is not broken. carry the material.

If you cannot take the batteries some where to load test then I would consider bringing another battery and should be able to run and start on one good one.

you would be surprised what strange things bad batteries can do. if you are running two batteries in parallel then disconnect them and let sit over night. check the next day and you will know if one has a dead cell. When connected together you cannot tell which is bad. bring battery charger with you also to make sure if they are good they are fully charged.

Rich