It sounds like the circuit board for your MaxxFan Deluxe Roof Vent w/ 12V Fan, Thermostat, and Remote - Powered Lift - 10 Speed # MA00-07500K is the issue.
I recommend replacing your circuit board with the Replacement Printed Circuit Board for MaxxAir Manual Lift RV Roof Vents # MA10A21276K. view full answer...
It could be a couple of reasons why your MasterTow Dolly is chucking when applying brakes.
I recommend checking the brake fluid levels and ensure it is not low. I also recommend checking the ball and coupler, and ensuring that you have the correct size ball, and that your ball isn't loose.
Finally, you could have a partner ride alongside you and examine the chucking, it is possible something on your hitch is loose and could be causing this issue. view full answer...