the fuse element inside my pre-glow timer relay is blowm. my "repair manual" states to test the glow plugs w/ohm meter set on 200 range. diconnect glow plug harness connecter at relay & go from ground to each numbered terminal in turn. any infinite reading on meter indicates a defective plug or it's correponding wiring. all 5 of my plugs are showing infinite readings. could they all be bad just like that? is there another way to check them. thanks for the help.[B)]