Ok so i understand after starting the voltage goes to 10 when grid heater is on and you can hear it lights go dim, no biggy.....
So getting off freeway I hear the humming sound like grid heater is on and voltage meter is around 10, dash lights ar dimming, but it is 55 degrees outside. Had been driving for 20 minutes truck is warm, im nervous the cold is coming. I did a search and could not find anything like this.
Recently replaced lift pump with FASS DDRP. Kinda lost thought about getting alternator tested, waiting to see what peps are thinking.

 

What kind of manuals do you use for maintenance and such? standard chilton?

 

Sounds like you may have a bad alternator. Don't check it when the grid heaters are active. Wait until they are off. Also, have your batteries checked.

 

I agree that it sounds like possible batteries or alternator issue.

I'm also a bit confused because your sig shows an 04.5 truck that no longer has a DPF??? Your truck NEVER had a DPF

 

The other thing it could be is a bad battery intermittently shorting. What condition are they in? Oops, i see this has been mentioned twice already^^.


It could also be a short not related to the battery. Depending on where it is it may not blow a fuse, but can ruin your voltage. Do the easy stuff before you go looking for an intermittent...they are tough to find.

Is there a fuel heater on your rig??

Chay