Best bet is to start by checking each of your glow plugs, use either the test light method or a multi-tester. The easiest way is to do the test light from the positive terminal on the battery, and touch the other side on the connecter on top of the glow plug after you remove the bullet connecter. If the light illuminates then you know you have continuity through the glowplug and it is somewhat working. The better way is to use a multi-tester and get an ohm reading off the glow plugs, it should be around 1.5 ohms if I remember right. After that I would clean all the connecters that attach to the glow plugs and install new ones if neccessary , I cleaned all mine and had to install 3 new connecters and I used pliars to squeeze the old worn ones together a little tighter to assure a good connection. After that check to make sure the ground wire is good and tight and last of all check the large rectangle connector on your pass fender well for slightly burnt connection. The system decides how long to stay on based on the resistance reading through the system and poor connections can really mess with it's decision.
