Only because I didnt follow stated path...your first post though was correct.
Panel on roof to controller (thru existing prewire), from controller to battery(s). It should be that easy on a prewire.
At approx. 10amps on good day, if wire really is 10ga your stylin, but given distance 'could' be slightly smaller. From controller to batteries (lower volts) is where you want to add as large of cable as controller will accept (usually 10 at best).
Many have posted using the prewire on a Lance.
I would check existing wires regardless, Resistance not a bad idea but more for power to ensure no one has tied into some where/somehow. Then tie wires at source and check on roof for continuity between +/-, it is 7+ years old.
But then I use Delo
