Electric Brake Magnets
When the electric brake magnet is magnetised it grabs the brake drum spreading the brake linings. As a general rule these magnets should last around 50,000km. Generally after 50,000km they start to wear leading to short circuits as the magnetic coil windings start to make contact with one another.
We often change magnets well before 50,000km and this is generally where customers have the non-pendulum brake control units. Non-pendulum (solid state) brake control units output the same signal to the caravan brakes irrespective of the cars deceleration so the majority of the time the brakes will be getting too much power. Essentially the non-pendulum units are prone to wearing magnets very quickly, plus making the brakes very hot which can cause other issues, such as premature bearing failure.