Thanks Ken and Bill for the welcome and your comments...much appreciated.
I just came in from outside scratching my head trying to figure out how to get
ANY wires through the firewall much less three!
Ken, you mentioned that you have a Grand Cherokee...do you recall how you got your wires through the firewall?
Bill, your thoughts about the ground make sense...even more so, now that you mentioned that the ground is just for the brake controller return. What got me wondering in the first place was that the ground for the controller was maybe a 14ga, if that, and the 12V in and brake wire out were 12ga.
Once again, thanks...