A career in electrical service work has taught me that while that is possible, it is not probable. A good tech should be able to verify the switchs with a quality ohm meter. Many people consider that a switch is either good or bad but they can also introduce some level of resistance that might effect the voltage supplied. A good switch when closed should introduce less than 3 Ω and should read the same each time it is closed. It should also read infinity when released.
Depends on the size of the wheel/hub and associated electric brake drum pads. The RV maker can skimp on brake capacity just like anything else. Anything to save a few dollars, especially in a place that most buyers will never look before purchase.
My belief is that you do not want to ever lockup trailer brakes, unless want to become a member of the jackknife club. That is why they give you a brake controller. Especially with ABS on the tow vehicle. Any wheel that is skidding, cannot be controlled. It may or may not follow the truck. If the trailer brakes lock up, your best hope is that the truck and trailer are in a straight line on a flat surface. On rain/snow days, I back the controller down a bit and leave more space in front of me.
The owners manual on my Ram 1500 says to set the gain so the trailer brakes lock just at full gain. I probably disagree with them. The truck has ABS so will never lock.
Just from my own experience with ABS on unplowed snow covered downhill roads during a hard stop. The tires no longer push the snow into nice big piles in front of them to help it stop, but they just make these little snow piles that the tires go right over, and so I keep on going, going, and going.
The brake controller that I use had instructions that stated that it should be set to the point where maximum manual braking would just slide the tires on dirt or gravel surface, then back off the smallest amount possible.
The brake controller they use on my truck say that they provide braking proportional to how hard/fast I step on the brake pedal, but they aren't supposed to be able to lock up even when set on the highest gain. I haven't been able to test that out because even though I've had the truck for 6 months, neither I nor anyone I know owns a trailer with electric brakes.
Yes, just barely sliding on sand or gravel is a good way to be sure you are braking hard but still below the pavement skid threshold. I've used that technique myself. Works well is you have access to the right type of surface and can pull the trailer there for a test run.
I don't know how the controller could guarantee that. It has no knowledge of the state of the actual trailer brakes or their adjustment, or of the road surface under the tires. It gets no feedback from the trailer wheels to tell it that wheel lock-up is about to occur. The gain control just limits the max amps sent to the brakes.
