Rough and long start grid heater?
 

I have a 03 5.9 dually that turns over/ cranks fine but takes a while for it to fire up just wondering if there is any way to check the voltage on the grid heater to make sure it's working. I have read a bit about the injectors and capping each one off on the Rail side just un sure which side that would be. If any of you have any other advice that would be help full thx in advance