Welcome to the forum.I have an 06 2500 with a Cummings engine ,so ive recently i noticed that my voltage gauge drops when im driving sometimes and the blower fan slows down then goes back to normal within the last year the alternator has been replaced and the blower fan and control module i have read that the fuel heaters can cause this symptom any input is appreciated thanks
If it has just recently started, then it is probably the grid heater because we are getting into the winter months and colder temps. It heats the intake air. It does not heat the fuel.
And yes, it is a cummins, not a cummings.
The grid heater is a high current appliance and it will cycle on and off several times when the engine is cold and the outside temperature is below 53 degrees. It is normal and by design. When you get in the truck this first time of the day, just turn the key to the on position, don't start it. You'll see a symbol lit up on the instrument panel that looks like a wire coiled up. That is the grid heater light and when it is lit it indicates that the grid heater is turned on. The grid heater light goes out when the engine is running, but the heater begins to cycle on and off, on and off, and the voltage gauge will drop and rise, drop and rise. It should stop cycling within a minute or two.