The fans are wired in parallel, so they both come on at the same time
There is never a time when just one fan works [ unless it is faulty]
So, you now know that the high fan circuit works
It is spec. to cut-in at 105/107
If it is higher , change the sensor you un-pluged
What u realey want to know, before changing anything, is if the gauge reading is accurate
[ simple resistance/temp chart verification w/ohm meter]
The low fan jumper should be done by pulling the plastic shield back and jump w/screwdriver blade without upplugging the wires.
You could be jumping the sw vs the circuit.
If still no fan , check the resistor behind drivers side headlamp.
[ also, when jumper sw, listen close for relay clicking.]