Hi TDK,
How was your volt meter connected ?1)Did you have one lead of meter connected to ground on the block and use other lead to measure volt at the nut of the glow plug? OR 2)Did you measure the actual voltage drop across the glow plug ?. One meter lead on the nut and the other on the copper wire under the insulator? The problem is this is a series circuit and I wish I could draw a picture on this site. Wiring is like this:
Black wire from indicator to nut on #4GP then the copper wire under insulator to under insulator on #3GP then copper wire from nut on #3GP to #2GP nut then copper wire fom #2GP under insulator to #1GP under insulator and then copper wire from #1GP nut to ground bolt on block. So if all the GPs are working correctly measuring between the nut and the wire under the insulator the reading on the volt meter should be close to 1.5V. So if your battery is 12V then the restistor/indicator drops 6V then there is 6V across all 4GPs, so 6V divided by 4 since it is a series circuit gives 1.5V drop per GP. You had 5.9V at black wire on nut of #4GP which is good. From your meter readings I think you had your meter connected as in question 1) above. Please repost with meter reading as in 2) above. Any GP that reads considerably less than the others is partial shorted and if it reads much higher then it has a high resistance and will cause the next one in sequence to not get enough current to glow, but if one is shorted then it will blow the one previous to it. Hope this is not to confusing.
JB2
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