Valley Power can be a good vendor. I have used them in Sacramento.
Perhaps they can provide or suggest a mobile service to get your rig moving to a repair shop?
Or, use your roadside assistance plan to get towed or repaired.
Note : Some wire harness setups can be used in several models of rigs. So the extra wires can be a normal byproduct of using standard wiring harness to save production cost if your rig does not need those wires.
Testing to see if the wire has continuity (an unbroken path) between two attachment points is done with a multimeter set to the Ohms function. One lead on the meter to each end of the wire.
(Using a cheater wire to one lead is common for runs longer than your meter leads.)
The meter then shows whether the wire path is complete or broken. A perfect run is shown as 0.00 ohms on my meter.
I suspect the loose wire does not need to be attached unless you see that it is damaged or a dangling wire close by.