Hey guys, I’m new to owning a diesel and have always heard you turn the key to the on position and wait a few seconds for glow plugs to heat up before you start one. I have an 07 GMC 2500 and the wait to start light takes quite a while to go out. I’m talking. 30+ seconds now that it’s cold and even took 15-20 seconds when it was warm out. Does this indicate new glow plugs are needed? The guy I bought it off of I’m pretty sure replaced them within the past few years. Thanks!