You can short a jack plug using a small piece of wire soldered between tip and sleeve. Sometimes you don't actually need wire and can bend the terminals together and then blob solder on.Dear Jon, Thanks so much for your help.
So, do I understand you correctly that
(1) I would have to solder a wire between the tip terminal and sleeve terminal to make a "shorted jack plug"?
(2) Do you know if anyone online sells "shorted jack plugs"?
(3) Should this shorted jack plug be connected to the Radial JDV in my setup above? or should it just dangle--attached to nothing but the return of the effects loop (other end dangling)?
If you can't solder you can get a cheap short instrument cable, cut it in half and twist the wires inside together and then cover with insulation tape. It's all very low voltage stuff so no risk of shock.
I don't know anyone who sells shorted jack plugs.
The shorted jack plug is just a plug, and it goes in the effects return loop.
Your setup should be:
efffects send --> Radial JDV MKIII Direct Box --> xlr to mixing board
and effects return just has a shorted jack in it.