Can anyone help me, I'm absolutely baffled had a starting issue with my derv. It's getting longer to start of a morning, checked voltage at plugs 3x 12v replaced the one sat at 0v with a brand new ngk one I had in my toolbox, the problems seems to have got slightly better but is still there... Today I checked resistance of them, all good but one of the ones sat at 12v shows open circuit, how the hell is this possible if it shows 12v!? I grounded the body of the one I removed the day before at resistance shows around 3 ohms, yet it was showing 0V when on the vehicle, basically saying open circuit!? I'm going to get some more glow plugs come payday on Friday, but I'm just curious as to what the hell is going on? Cheers in advanced