Correct
The electric brake controller, on vehicle dashes today, does nothing for most marine trailers. Most are Surge operated by compressing the brake coupler against the ball. The force on the hitch ball then compresses the master cylinder, inside the front coupler, and presses the fluid into the wheel cylinders to enhance stopping. When functioning properly they work excellent and will improve stopping significantly.
On a 2021 model it’s filled with DOT 5 brake fluid, and you must add DOT 5 if the reservoir is low. Of course if the reservoir is low, then it’s going somewhere and the leak must be found. The system may also have to be re-bled after the leak is repaired.
Of course, these systems age in time and trailers notoriously get ignored on requiring service. Older ones (2019 and back) also rust inside the brake fluid as the older fluid absorbs moisture (hygroscopic). This simply occurs in time and anyone who’s worked on an older vehicle will relate to this. Boat trailers seldom get brake work done or the fluids flushed, which is why we switched to DOT 5 fluids. We also don’t have pulsing by the anti lock brake systems that froth DOT 5 fluids in vehicles. It’s consistent pressure and DOT 5 works great for surge brakes.
On older brake systems (Bass Cat or other) they should be regularly flushed and new DOT 3 fluids added. All DOT 5 systems have a label on top of the front coupler noting those as DOT 5 and reminding you to depress the safety cable tab. There are two (2) labels to remind you to depress the safety cable tab.
hope this helps,
BCB
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