truck cranks fine and idles fine but last night the lights went dim and voltage meter got down to 10 but after about 10 mins lights got bright and voltage was showing over 14, could this be bad batterys or alt the voltage regulater is controlled by the PCM. ANY IDEAS

 

The grid heater on your truck causes this. it draws a massive amount of amperage and will drain your batteries preety quik. They usually shut off at 18 mph or when intake air is at a certain temp. Not to worry every truck with the grid heater will do it when its cold outside

 

Read this:

https://www.dieseltruckresource.com/...ad.php?t=57485

It's the first thread in the HELP section.

 

any ideas why voltage is reading over 14 it has always read 14 on the money could it be overcharging?

 

I just pulled codes and I am getting code 47, charging system voltage too low. could it be seting this code when the voltage is dropping down to 10?

 

I know my grid heaters are supposed to cycle and they usally do, but this time lights stayed dimed for the first 10 mins of driving their was no cycling. But it does act like its warm up related because it has happened twice and they started working at the exact same moment when driving. This may be normal but I have never experienced this in the last 4 CTD's that I have owned. In that post by shovelhead their was one post by somebody wanting to know why his voltage dropped to 10?

 

I first inclination is that it's time for new batteries.
I'd get them tested.