I'm having an issue with a trailer I recently purchased. When I step on the brakes, 2 wheels instantly lock up. It's wired correctly, do you think my brake controller is going bad? 
It worked when pulling another trailer a year or so ago without issue. Don't want to spend the money on a new controller if it's something else.

check the two brakes that are locking up to make sure the front and rear shoes aren't reversed.

Hi BF,
with the electric trailer brakes I had anything to do with they had a means of adjusting the level of braking to prevent this for different weight or road surface situations--maybe yours is an older controller without this ability.

Knowing the brand of your controller may help to find an operators manual that some one kindly put on line.

Wheel bearing grease saturated linings or rusty drum brake and magnet actuator arm lining surfaces can cause this as I found with one of my tandem Caravan/ trailers when I purchased a used one.
Did the old trick of gently heating the linings several times, with the oxy to make the oil exude out of the lining material until it stayed dry.

Cheers,
Eddie B.

that's what I was wondering about, if the wires were broke to the other two wheels would it cause the 2 to lock up?
The controller does have the gain adjuster and it is at minimum and still locks up.
Need to get it into the shop and pull all 4 wheels to figure out what is going on with it.

are the two that lock up on the same axle? or different axle same side? or different axle different side? i don't think it is your controller..

Very common to need to adjust controller different for empty trailer and loaded. That is why the adjuster is there. But maintaining the wiring on electric brake is a ongoing thing.

Many trailers the brakes are not auto adjusted for the distance of shoe to drum, so you need to do a old type manual adjustment on the brake shoes. That could be all that is keeping the other brakes from locking as well.

only one axle locking may not be a big issue a lot of trailers only have brakes on the front axle.

electric brakes can be pain in the arse to set correctly. first repack or replace the bearings and seal use timken, koyo, skf or ntn bearings the cheap ones just dont last. the difference between ford and gm pattern hubs and axles is the outer bearing, ford is larger but the bearing will fit in either hub you simply choose what suits your axle.

a few common issues the drum is rusty from sitting idle wire brush and emory cloth to smooth

the brake shoes are not adjusted or the mechanism is jamming lube the sliding sufaces of actuator arm and shoes SPARINGLY with high temp anti seize. dont lube the magnet face just the centre bush. worn magnets also cuase problems. adjust the shoes.

the controller could be set to high or be faulty. from what you have described its either the brakes are fualty/out of adjustment or the controller is stuffed.

best fix piss off the drum brakes and go electrically controlled hydraulic discs yes it cost money but they give much less problems and need less maintenance. alko make a system that is very good. theres a couple of other brands too.