When you pulled out the relays was there any green corrosion in or on the terminal ends of the distribution box?
I have found a few pdm's that got moisture in them and corrodes and cross feeds power to other terminals or causes low voltage issues.
And in a number of times chassis modules had to be replaced,known issue with diamler/chrysler or freightliner modules covers not sealing correctly and was a recall to replace covers to a newer design.
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