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The fact it is making the normal 14v output tells me the regulator is at least partially working, driving the SCRs properly to maintain that voltage.

Yep, sounds like the voltage regulator On top of the alternator housing. You can confirm this If you unplug the regulator and start the truck. the alternator should go to no power output Which will confirm the field is not shorted to ground inside the alternator chassis. This alt feeds 28V to...

What’s that large cable hooked to the alternator ground point?

Yes it does, and that strap is probably THE most important ground on the truck... basically it is the main neg path from frame to-from the batts as the engine and trans and exhaust are isolated on rubber mounts. Not sure how good a path is provided thru the engine... I recall a,no start issue...

Yea, that starter terminal looks pretty ugly...

Actually the shunt is mounted right beside the polarity box(toward the rear). I am sorry, I should have mentioned it before but wasnt thinking about it... The main Ground lead and strap run right under the starter...

Also check the instrument shunt conections(Under/inboard of air filter) The neg lead runs from the batts to the shunt, the other side of the shunt runs to the starter case. At that starter connection there is a ground strap that connects over to the left frame rail...

Thats weird... What does it measure at the alt when you are getting 14.5 and 17 at the batts? That totals 31.5, and shouldn’t really be possible, unless the regulator has issues...

There is a small vampire load from the 12v to the transmission... here are my two battery voltages when idling... 14.23/14.42... i have a solar panel, a simple buck converter set to float the 12v batt(the one with the vampire on it) to 13.2v when the sun is out, and an equalizer that holds...

Yea because of the variables, the only real accurate voltage measure of a battery SOC are the conditions listed in column 1, and then only after the battery has been setting an hour or more for the electrolyte levels to stabilize in the cells... i think you will probably find a bad connection...

The alt doesn’t know nothing about charge rate. Simple straight voltage regulation 14.1/28.2v. it should deliver this rain or shine, all day long regardless of load changes until the load is so great that it cannot maintain voltage and the voltage starts to fall away from that regulated...

you could have a battery that is breaking down with current applied and loading the system Beyond limits. Since the 12v is low, I would suspect one of the outer 0-12v batteries. I would start by disconnecting 2 batteries at a time, one inner and one outer(Like opposite corners). And see what...

Well I wouldn’t call that right... This thing should be delivering 14.1 and 28.2V Your 12v is nearly a volt low(13.2 is a long term float voltage). Your 28v is more than a volt high, so something is outta wack... if you measure the running voltage on all 4 batteries I think you will see what...

Yep, this alt is sensetive to what it sees on the other end of the line. If it doesn’t see a good 12-24 relationship, it will just pulse as it continually tests to see if the batteries are valid so it can charge them...

The wire with the yellow heat-shrink on the forward reg terminal feeds 24V from relay K11 when the oil pressure goes over 15 PSI. Looks like it is being told to generate. The terminal with the red cap is a field sense output. In your A0 it doesn’t do anything except feed up to the STE...

which is why the later/larger LMTV alts are not necessarily backward compatible as they interact with the LBCD which the A0’s do not have...