CUCV M1009 Passenger-Side Alternator Gremlin (yeah yeah, I know)

[number9er]

CUCV M1009 Gen 2 Light Gremlin (yeah yeah, I know)

Despite the overabundance of information on this site about this subject, I'm posting this for several reasons. First, I think it's handy to have some of the history of my vehicle and its various issues documented here for posterity. Second, if some of you more expert users do find yourselves perusing this thread and happen to see something that sets of a red flag that I somehow missed, I would be eternally grateful for a heads-up. And lastly, for your entertainment, as when you see some of this, you may just have to laugh.

So I'll start with a little history: I bought this M1009 earlier last year. You can see a short rundown of the existing issues in that link (my SteelSoldiers intro thread). Among them:

"Passenger side alternator was replaced on the first day. A week later, positive terninal broke off and shorted the leads to the alt body. Melted a big spot on the back of the alt, but amazingly didn't cause a larger fire or even damage the alternator further. Had it checked out and terminal replaced for about $50. Seems to work (mostly), although now I have a dim pulsating Gen 2 light when running."

Here are some pics I took of the alt around that time:


I watched that Gen 2 light pulse and flicker all summer and fall until finally it just stayed on full bright. The truck continued to start without problem until it started getting really cold out. I guess it worked off of the last bit of charge the rear battery was able to get until it really needed some extra amperage. I was able to jump it off and then manually charge the battery after every time I drove the truck. Finally I ordered a new/rebuilt alternator from NAPA. I took my Ohm meter up to the shop to test the ground before bringing it home and of course it wasn't isolated. The fiber washer was there, but it was making contact somewhere. They were very nice and patient with my explanation of what the meter should read, and had another overnighted from Knoxville. It tested out great. I picked it up yesterday along with some 12 gauge fusible link wire - which brings my to my next concern...

When I bought the truck I noticed that the 8 gauge 12V + wire coming from the negative terminal of the rear battery was duct taped right where it meets the 12v diamond-shaped terminal on the driver side firewall (I really should have taken a picture). It always bugged me a little, but as far as I knew, it wasn't causing any problems and I had my hands full fixing everything else. I decided to make a new fusible link before installing the shiny new alternator. Look was was under the duct tape:



Someone took what was left of the fusible after it was fried at some point and just kinda tied it together and wrapped it in duct tape. So my concern is this - Is there some other undiscovered issue that's going to immediately zap the new alternator? Hopefully my new fusible link will do its job if it's needed. And I've done the troubleshooting from the TMs as well as several hours of my own testing with the voltmeter. Everything checks out, though I wish my battery cables were in a little bit better shape. They will have to be rebuilt soon. I just have to wonder why it seems like this truck is where passenger-side alternators come to die.

Anyway, it's been way too cold to bust my knuckles putting the new one in for the past couple of days. I'll keep y'all posted.

 

[number9er]

I got the new alternator installed. Now I have a dimly lit Gen 2 light again. I'm running out of things to try short of rewiring the whole charging system. I've done the troubleshooting in the TM -20. Both batteries appear to be charging. They both read a little north of 12V when not running and a little north of 14V when running. The only other clue I have is that when I turn the key, the volt meter bottoms out. I mean it goes from floating over to the left to pinned all the way down to the left. I replaced the resistor with a 300Ω resistor from Mouser. Not sure what's up there either (actually just put the new one right over the old one).

Ideas?

 

[MarcusOReallyus]

Somebody just posted about that sort of issue a couple of days ago. You might want to check out that thread.

 

[number9er]

Thanks Marcus. I did read that thread. I've checked the posts and this is a brand new (rebuilt) alt. It's doing the same thing the previous alt did before it just finally went bad.

By by the way, I also read your resistor bypass thread, and penciled that in for a near future update.

 

[number9er]

The exciter connector looks a little cruddy. I think I'm gonna go grab a new one at Advance or OReilly. I'm starting to wonder about the diode between the Gen 2 and Gen 2 relay. It doesn't seem like that could be the issue because the exciter plug tests out ok with ignition off and on. But maybe it's grabbing a weak ground somewhere after the gen 2 relay besides inside the alternator.

 

[dougco1]

Have you load tested the batteries? Some times they can read normal voltage but still have a bad cell

 

[number9er]

Yeah I bought a load tester at Harbor Freight and tested both batteries and they test great. The positive cable terminal on the front battery looked really bad (several strands of copper broken). So I cut that back about an inch and put one of those screw-down clamp terminals on temporarily until I can just build a new cable set.

 

[number9er]

I had said before that I may be getting a weak ground between the gen 2 relay and the alternator causing the gen 2 light to glow, but that can't be the case because when I pull the exciter plug, I get no gen 2 light. That means the grounding is happening inside the alternator. So I've either got a bad alternator (for the third time in a row) or something elsewhere in the charging circuit is causing the alternator to ground the brown wire. This is where it starts getting murky for me. Would a bad connection somewhere in the charging circuit causing resistance make the passenger-side alt complete the gen 2 light circuit? Is my next step to replace the battery cables and alternator cables?

 

[number9er]

Replaced the exciter plug. No change.

I took my voltmeter off and tested it with a little 12v AC Adapter. It works fine. Looking at F-4 in the -20 TM, I think someone just hooked it up backwards. I switched the terminals on the back, so I think that's fixed. Small victory, but at least something got fixed today.

 

[number9er]

Checking the batteries again, my battery charger showed the rear battery at 13.3 V and 95% charged. The front battery showed 12.2 V and 83% charged. I'm charging it with the charger now. Would that difference in charge somehow cause the passenger-side alt to light the gen 2 bulb? Anyone? Bueller?

 

[dougco1]

Checking the batteries again, my battery charger showed the rear battery at 13.3 V and 95% charged. The front battery showed 12.2 V and 83% charged. I'm charging it with the charger now. Would that difference in charge somehow cause the passenger-side alt to light the gen 2 bulb? Anyone? Bueller?

You should disconnect and fully trickle charge both batteries. I still think you have a bad battery that is not taking a charge from your alternator.

 

[number9er]

I'm in the process of that now. I charged the rear battery this morning and started the front battery a few hours ago. When they both read 100%, I'll hook it back up and see what I have. They both tested ok with a load test a few days ago, but you may very well be right. And Harbor Freight load testers may very well be made by children in Southeast Asia.

 

[number9er]

Full charge and no change. I'll take the batteries to O'Reilly's to be load tested on a real machine tomorrow. So frustrating.

 

[iasc399ia]

Sorry to hear about all your issues. Unfortunately I can't help as I am new to the MV game and am no mechanic, but hopefully someone chime in to help out.

 

[number9er]

There are tons of threads on this same issue on this forum. I've been through them all. At the very least, I've learned a lot about how the CUCV electrical system works. This forum is really helpful for sure. I'll get it figured out eventually.

 

[number9er]

Finally had the batteries tested today. They had a full charge and passed all of the tests with flying colors. Gen 2 light seemed dimmer today but it's definitely still there.