Good observation, thanks for that reminder. The “fail to pass enough current” comment resonated with me, as a fellow Jag-lover had a situation several years ago that resulted from a relay failing to pass adequate current. Here is a link to that thread if you’re interested (warning - it is lengthy, with 193 posts):
Back to the topic at hand, I noted the resistance you spotted when checking the ground connection through the boot light switch. My boot light is working, albeit perhaps not as brightly as it should, and as I was in a hurry I did not pursue the matter. There does appear to be some corrosion around the switch where it mounts to a bracket so that may be the culprit.