connect the ground end of a test light to the pos. side of the battery. now un hook the wires from the glow plugs or unbolt the terminals. after u have done this touch the tester to the glow plug...
You can test each glow plug while still installed in the engine. Just get a test light and connect it to the positive terminal of the battery and touch the point of the test light to each glow plug...
This test will determine what glow plugs are working. ( It will not determine a partially burnt plug ). Disconnect the glow plug wires at the plugs .( You must unplug all of them for this test to...