My e300td is cranking but not starting. Battery good and i changed the main fuel filter. The number 6 glow plug is not working and stuck..thats another story. I gave up and had it towed to mechanic who said removed air from fuel system and car started. This morning same story, car cranks and does not start. The car was not starting before I changed filter so i figure a leak somewhere at the injectors?

When you pull plug out of glow plug relay and put multimeter how do.you test for good or bad plugs at the 6 pin plug?
Thanks