I do not know the layout of your engine, but if you can reach each plug, the easiest way is to compare the ohm reading on each plug with the ohm reading of a known good plug. Test the known good plug by putting one lead of your multi tester on the plug contact pin, and the other lead on the glow plug body. To test the ones in the engine, just remove the wire from each glow plug, put one lead of your multi tester on the glow plug contact pin, and the other lead on the side of the glow plug body. Should give you approximately the same reading on all plugs if they are good. Good luck....