Yeah, no solenoid needed, or wanted. You need varying voltage, actually current, going to the brakes to control the amount of braking that happens. The breakaway is just a 12 volt car battery in a box on the trailer. Does not even have to be a big battery.
Its grounded to the trailer and hooked to a simple switch. The whole thing works like the breakaway lever on your surge brakes. If the trailer comes loose, the small cable or chain hooked from the switch to the tow vehicle pulls a restraining pin out of the switch. The switch is spring loaded inside, and when the pin pulls out, it connects the trailer battery to the brakes which causes them to go to full power.
You will need to pull the drums and check the brakes on the trailer just like you would regular drum brakes. They have shoes that will wear out.
But there are one or two differences from your regular truck drum brakes. First, in some trailers, you have to pull the wheel bearings to get the drums off. But there is nothing special about how the bearings come out.
But, there is one wear item that you do not have on truck brakes. That is the "puck" on the end of the actuating arm. It slides along the plate, and the more you apply the brakes, the more it scrubs. Its unusual for one to wear out, they last a good long time. Probably will outlast several shoes, but sooner or later they will wear.
As long as it looks intact, and no wires are showing, it should be fine.
Here are a couple of pics. Other than the arm with the electromagnet they are fairly regular drum brakes.
