I hate to be a Nay sayer here, but unless there is something that is deteriorating in the way this harness was connected, I wouldn't jump to the conclusion that this is your problem.
(still needs to be dealt with)
Running a wire in parallel with the HV pack won't create an error code.
And there are only just so many ways to screw up a pair of wires.
At 380 volts DC or so, a short would be kinda self diagnosing, what with the fire and death and all, and an open would be... well what you have anyway.
Everyone who put an auxiliary battery or a second charger (brusa) in tapped parallel to the pack, and no error messages resulted.
I'm just saying....
When we installed our Brusas (in the front), we went into the inverter housing on the U.S. Passenger side.
There is a location to do a nice clean connection inside.
If they did that, they most likely entered through a gland (boot) on the rear of that passenger side, which has some delicate wiring close to it.
Maybe in doing that, they created a situation where these heavy conductors are rubbing against the really little control wires and that's where you errors are coming from.
You can see the heavy conductors from the pack )factory) on the left of the picture, and all the myriad of little control wire nearby.
Well, good luck, and I will wait to hear how it works out.
