[licenced2burn]

So my truck is wanting to charge at an idle when you first start it up and until you start driving it and sometimes takes a mile to get up to 13v on my cts. The alternator is only about 3 weeks old and batteries were new last april and the alternator is a 139 amp. I went with the bigger one because i went threw 3 110 amps in 24 months. The only aftermarket electronic item i have in hid headlights and i pulled the fuse out on them and it didnt change anything. The only other thing im thinking is the posative cable on the drivers side looked like it has oxidation in the end of the wire so i sprayed the terminal cleaners in the end and waited and hour washed it off and started my truck and it was charging 13.3 so i plugged my hid's back in and turned them on and it went up to 13.5 and now today its back to not charging till im driving again. I wouldnt be to worried but when its not charging my ficm is reading arounf 42v and its a 58v swamps ficm. And my voltage will read 11-11.5 till it starts charging. I have unhooked my batteries and voltage and load tested them and the voltage held at 12.6 when they were unhooked and load tested fine i beleive they are 1000 cold cranking amp batteries. It sounds like the wire might be corroded to me but is there a way to test it? And could that make my truck not start charging till im driving

 

[mhatlen]

You know that with these diesel engines when you first start it the glow plugs run through thier cycle for approx 2 minutes and they can draw up to 180 amps.
Because of this the alternator does not charge until glow plugs are off, around 2 minutes.

So take a look at the volt guage and you can see when it starts coming up on power.
Your ficm has a problem now, at 11.6 volts is plenty of power to run the ficm

 

[licenced2burn]

When my alternator is charging the ficm reads 48v so I hope my ficm isnt going bad it just went out of warrantee in september. I saw that it didnt start charging till the glow plug shut off but i was under the impression that was when the light went out on the dash but that could explain the charging issue.

 

[mhatlen]

You should not be seeing the alt light at all period.

Start with testing the batteries, you may want to put a charger on them overnight and see how well they take a charge.

Once you do that see what your voltage is cranking and then see how well it comes up after alt is on line.

Of coarse check all cables and grounds and grease all the terminals on the batteries.

Being you are seeing the light come on after you start it, I would be looking at the batteries very close because my guess would be they aren't holding a charge.
Always the possibility you have a draw pulling them down just not as likely.