M1083 '98 Alternator/regulator troubleshoot.

[Grimbo]

On my 1083, replaced the alternator and regulator app 50hrs back, been running 100%. Started up this weekend and voltmeter was 25v and would raise with rpm, whereas before it would be 28-30v continuously, idle or higher rpm. Got the TMM troubleshooter for alternator, all fingers point to regulator but not 100% sure with what I'm seeing.
After starting app 1min, it would go from flashing green on both top flash amber on one then both, then intermittedly go back to green(engine loads up), then back to amber and stay there. Amp output increases with engine rpm(very low output at idle). Armature is magnetized while flashing amber. Jumped 28v to E term on regulator with no changes.
No noticeable voltage drop from batteries to alternator.
What I did find on intial troubleshoot was jumper between two start batteries was loose to be able to move it freely, but not enough to break the contact. My thought on this that if the start battery was disconnected while charging, was that at worst the alternator would have blown diodes, but on the test that seems fine.
So im thinking its the regulator and why would it fail within 50hrs of use. Thxs
Links are videos of what I was seeing.

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[NDT]

What year is your truck? It’s not a 1988.

 

[Grimbo]

What year is your truck? It’s not a 1988.

You are correct, it’s a ‘98

 

[NDT]

Suggest you check the connections on the reverse polarity protection device under the spare tire. Also verify that the excite voltage coming from the oil pressure switch is constant.

 

[GeneralDisorder]

Check ALL your battery connections, the PPD connections, the alternator connections and EVER SINGLE ground you can lay your tools on. Chances are the regulator is having a hard time from bad connections. These brushless alternators respond very slowly to load changes and being you have an A0 truck without the battery load disconnect it is possible for intermittent connections to the batteries to draw lots of amps and then suddenly not be connected over the next speed bump and cause the alternator to overshoot it's voltage target before the VR can bring it back under control.

Too long under these conditions and you WILL need a voltage regulator or an alternator or both. These trucks need constant attention to their charging ecosystem and all the connections. If you don't have NEW battery cables I highly suggest you take advantage of these (looks like a sale for the 4th).

https://midwestmilitaryequipment.com/replacement-battery-cable-kit-for-lmtv-mtv-fmtv/

Not typically a fan of MME but the price on these is fair.

 

[Ronmar]

Yea the alternator relies on a good connection to a series wired 24v battery And the 12 from the middle.. as mentioned check ALL the connections.

one way to confirm connections is to take actual voltage drop measurements. You need a piece of wire long enough to reach between battery and alt. Doesn’t need to be large gauge, comparable to the lead wire used by your meter is fine. Test for voltage drop on all 3 pathways(gnd, 12 and 24) by connecting the long wire at the battery ground, and then connect the other end to your meter over near the alt, and the other meter connection to the ground point at the alt, start the truck and with the meter set to read DC voltage. This will read directly, the voltage developed across the resistance on that path. Putting a load on the battery will help show any weaknesses. Repeate the same test shifting the wire ends to the battery 12 and the alt 12, and battery 24 to alt 24…

 

[Grimbo]

Suggest you check the connections on the reverse polarity protection device under the spare tire. Also verify that the excite voltage coming from the oil pressure switch is constant.

Yes, I took the reverse polatiry isolators out a while back, they cooked up. Will check the excite voltage to be sure.