2005 vnl 670 overcharging batteries

Hi guys i need help with this one problem.my truck is overcharging batteries and its reading 14.9 i know this is not normal.i changed the alternator and checked the batteries today and now its reading 14.5 idling.this problem is happening on wet pavements.please help

 

I cleaned all the grounds and this is only happening on wet weather.i thought it was the alternator but after changing the alternator i still have the same problem.

 

Am geting the over charging warnings on the dash.yesterday at some point it overcharged up to 15.9, i pulled over and stoped for like 5 minutes with the truck off and then took tbe next exit to the shop.they mesured the batteries and cleaned all the terminals but the problem was still there.i decided to throw in a new alternator straight from volvo and here i am with the same problem

 

Its sometbing to do with wetness.am gonna check the wiring harness and see if there is anything

 

I appreciate all of you for trying to help me out.

 

Come to think about it,this issue is only when the roads are wet and and maybe the ground wire is geting wet and loosing the connection.am gonna wait untill it dry and go check underneath and see if there is some weird corrosion under there.i dont know where the ground wire is mointed but i know is somewhere inthe flame