there's two rcs labelled "distort footswitch", one "L" and one "R" . I tried to jump them with a rca patch cord and go he results above. Then I tried cutting a cable in half, stripping the wires and joining the lead grounds to hots to make two shorted, single ended rca plugs, result: one lowers the volume, both lower the volume, the other ( by itself) has no apparent effect and in no case does the front panel distortion distortion control have any effect...
Oops... sorry I misread.
You do not want to jumper the two RCA jacks together. Not a good thing.
#1 Ok... the jack one that lowers the volume. Plug your grounded lead into that one and try turning the distort control. If it is working correctly, this should be the boost control and you should get MORE boosted volume as the distort control is turned towards zero, less volume as the distort control is turned towards 10.
#2 If that works, take that SAME cable, unplug it and plug it into the other RCA jack. This should turn on the distortion - and the distort control should give you more distortion as you turn it towards 10.
If #1 doesn't work, then #2 isn't going to work either. Use your other half of the cord and try #1 again.
If #1 works and #2 doesn't... well, the RCA jack could need cleaning or could be disconnected internally, or the pot could be bad... or etc.