[will slow gto]

Hi Folks,
A couple days ago I was driving my 69 GTO and noticed whenever I pressed the brake pedal, the underdash courtesy lamp and dome lamp would come on. Checking the fuses, the 20 amp 'Stop' fuse was blown. Popped another fuse in and it blew again in short order. I noticed that when the dome lamp came on along with the courtesy lamp, the dome lamp bulb was very dim. Started searching for some threads on here and one or two indicated they may have had a short in the dome lamp harness. Other posts indicated some slight oxidation on the contacts in the fuse block could be increasing resistance. I disconnected the dome lamp harness from the tail lamp harness and took some 200 grit sand paper to the 'Stop' fuse and also the 'Dir Signal' fuse as that had blown too and I no longer had turn signals. This improved the situation slightly but both ended up blowing again after a few miles of driving. The car has 64K miles and the only wiring harnesses that have been replaced are the engine harness and the forward lamp harness, but those were replaced about 3K miles ago. Perhps it's just coincidence but a small chunk of black rubber fell from underneath the dash about the same time these problems arose. I've included a photo of the small piece of rubber (next to key in pic), maybe someone recognizes where it might come from, are they related(?), I'm out of clues for now. Thanks for your consideration.
Will