I disagree on the bad cluster ground. Only 2 items are working improperly. A bad cluster ground would affect many cluster items. It is posible that there is a breach in the circut board (I just repaired this exact problem in a 64 Fury). But I still think the running light circut is seeking ground in the cluster. Perhaps thru the fuel gauge sender circut as well. I don't have a diagram in front of me right now, but if the cicut bard looks ok I would go with my original diagnosis. A bad ground is by far the most likly culpret.
Doug
Dou8g