On those type of circuits a burnt trace is generally VERY obvious and hard to miss with just a visual inspection; Fractures are harder but as this isn't subject to much flexing it's a moot point.
I don't recall the test procedure, however I'm sure it's not very in depth. I suggest you use the TEWD and follow each end back to it's source trace where the harness connects. Check if the couple circuits you're having trouble with share a common trace.
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