Yes, you will only need to run one blue wire from your brake controller to the 7-way connector on the back of your motorhome, this wire is what takes the signal from your brake controller to your tow dolly to tell your dolly how much braking power should be applied.
I attached a link below that you might find helpful when you are wiring up your connector, I also attached a picture to the right that shows how you should wire the 7-way connector on your motorhome. view full answer...
Larger motor homes typically do not come with the brake controller wiring installed. The first step I would take is to make sure that the connector you found on the motor home under the dash is indeed for a brake controller. If the connector on the motor home matches the connector you purchased, then you should be able to plug in the harness and test the pins for the black and the red wires using a circuit tester like part # PTW2993. The black wire should show 12-volt power all the time,... view full answer...
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