When I first start my truck my volt gauge takes 30 seconds before it even moves, then when it does it goes up to 16 then drops to around 12 and keeps doing this for a minute or two then it goes to around 15 and stays there like it is supposed to. It doesn't matter if my headlights are on or not but if they are they get bright and dim as it fluctuates up and down. Do any of you guys have any idea what could cause this? Thanks in advance.

 

sounds like your grid heaters in the intake are doing there job .... does it only do it when cold ? or first start of the day ? if so ... its your grid heaters .. no glow plugs just an intake heater to help it start..

 

^what he said. mine did that same today at -30C.

when I'd hold the manual switch on my powerstroke, it'd do the same as well.