Agreed with what everyone is saying so far, but the "emergency" brakes you mention is just a switch to apply full power to the brakes when the key is pulled out. It's not like a car where there's a separate emergency brake system- this one is just for breakaway and not designed to be used when parked- in fact it's dangerous to use it when parked. But the brakes activated by that switch are the same ones controlled by your vehicle, and as others have said, you need a controller in the vehicle to adjust how much power goes to them.
Did you recently change tow vehicles or have the trailer serviced?
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR