I have a john deere diesel gator with a yanmar 3 cylinder motor. It is very hard to start in cold weather. phoenix az 40 degrees the low! i checked glow plugs they are good. checked voltage going to glow plugs was only 4 mv. not enough i guess so i put 12 volts to them for 3 to 5 seconds and the gator will start right up. so i replaced the glow plug relay/module and it still is only sending 4mv. not sure if that is how the glow plug system is set up or what my problem is. Any help is appreciated!!