Hey again.... out of curiosity I did an autopsy on the 606 foot pedal, expecting to see a housing for carbon discs and instead found that the inside looks like photo you posted earlier in the thread (the one with the junk in it). I'm guessing that those are the nichrome wires that DonnaMiller described in her reply - I've never seen the inside of one of those before (I think I had one once for a Pfaff 230 but replaced it without ever looking inside, it also got red hot). Interesting.
I boldly took the 606's stitch length lever and knob apart earlier - so now I know how it works (almost losing the smallest spring I've ever seen in the process) - and will give it a go to see if I can fix it over the weekend. :-)
Thanks for the info & encouragement. I'm a braver about working on the old Singers because the parts are easier to get.