I have a 07 F350 that think has a bad cab ground wire.
I put in a new 220 amp alt. and upgraded all the battery cables to 2/0.
Now when I start the truck the volts are at about 12-12.5 and then when the glow plug relay cuts out the volts jump up to and bounce between 14 and 15+ for a second before they settle down at 14-14.5 volts.
I have checked and cleaned the grounds on the block and frame.
I am stumped.
Thanks.

 

To save itself the Alternator does NOT turn on untill the GlowPlugs have cycled and shut off this canbe upto 2 minutes depending on ambeint temp no worries here

My truck does the same but when its charging It Hits anywhere in 14.0-14.6 volts range

so your 15volts does seem a hair high but sounds like its only a short time at 15.0volts so probably no biggie

there is a Ground strap passenger side from the FRAME to CAB right under passenger seat under truck just about inline with the Powerstroke 6.0L emblem on the Door

 

Thanks.
Today I also noticed that when my window is closed and I hit the power window button to make sure it was closed the volts jumped up to 15+ so that is why I am thinking it is a bad cab ground.
I will check that ground tomorrow.
Thanks

 

there is also one that comes off the ground from the passenger side battery to the fender well behind the battery

 

I also upgraded that one to a 6 gauge. Thanks
This is just driving me crazy.

 

Mine does the same thing I haven't been able to figure out why. If I'm driving at night with the lights on and hold the power window button my lights will get brighter and go back to normal as soon as I let off the button.

 

There is a ground on the back of the passengers head to the cab on 03-04,not sure if it is there on later trucks but would assume it is.