I have a 2008 Ram Hemi Quad Cab 4x4. While driving and decelerating, my headlights dim at 40 mph, then come back to full brightness. It's as if there is a momentary heavy electrical load on the system, but only while decelerating and only right at 40 mph. Has anyone else ever had this problem or know what the cause may be?

 

Start by getting your charging system tested.

 

 

You notice it happening at 40 mph. More importantly: 1) what is the engine RPM when this is happening 2) what gear is the transmission in. 3) what is the engine RPM and transmission gear when things go back to full brightness. 4) what is the age of the battery.