2012 Western Star charging problem

2012 Western Star DD15 Delco alternator, I'm driving in the dark in the morning and the lights suddenly go brighter and heater fan speeds up, I look at the voltmeter

and its pegged out at 16 volts, it does this for 3-4 seconds then drops back to 14 volts where it usually runs. It does this again about every three minutes, so I head for

the barn because I'm imagining burning out the ecm or lights etc. I watched the datastar readout and it showed 17.5 volts when it would go into

hypercharge mode. So I call my local western star dealer and ask if alternator chargeing is controlled by the truck computer, he tells me not that he knows of, so I buy a

new alternator and put it on. Go down the road about 20 miles and same thing, voltage pegs out for 3 seconds then back to normal. This time it only did it 3-4 times then

started working normally for the rest of the day. I don't think its an alternator problem. Can anyone tell me whether alternator charge output is controlled by built in

regulator or does it go through a computer?

 

Todays update-- and thanks to everyone for the useful suggestions. Had a driver on the truck all day and it never missed a beat. The answer to some of the questions asked- 1--It's a delco remy alternator, but I put a new one on and had the same issue afterwards, so I don't think its the alternator. 2-- the truck does not have an apu or inverter 3--I didn't test the batteries but i did put a hand on each to make sure one wasn't going nuclear, they were all cool and there is no problem with cranking and the voltage is good. 4--Yes it was raining but I'm on Vancouver Island and it seems like it is always raining. I think my next step will be to check and clean all battery connections and check out that remote sensor fuse Chip S mentioned, maybe clean any ground connections I find. One other thing I noticed when it would start an episode I would hear a faint click under the dash almost like a circuit breaker tripping, but the voltmeter never dropped, it would just go to max then return to 14 volts after a few seconds. Will update when I find something.

 

Update 2- Still have intermittent high charge, but have narrowed it a bit. Cleaned all battery connections, load tested the batteries, checked the remote sensor fuse.

It now appears to go full charge when the heater is on defrost and the cycling of the air conditioner kicks in. Also if I set it to any other vent/heater combo it is fine
but if I turn the air conditioner on it goes to full tilt charge, so I'm thinking maybe the air conditioner compressor clutch or wiring going to it. I have noticed a click noise when it goes hyper and wonder if that's the a/c circuit breaker resetting, then the big charge until the breaker blows. I'm assuming it has a self resetting breaker.Will post again when I have more info.