How not to trailer

[oil pan 4]

It doesnt.

[slowmover]

It does. They tap the brake fluid lines. That's enough to throw off the ABS signal.

One can make it work, but have to quite careful.

[oil pan 4]

They haven't tapped the brake line since the 90s.
With the advent of accelerometer base electronics there is no need to tap the brake line. It's been decades since the last time I saw a brake line tap brake controller for sale in a store.
They're probably still out there but they generally are no longer used except maybe by old people who need replacement brake controller for an old vehicle.
Why do you think electric brakes are still so widely used, they aren't only being used by people with outdated vehicles.

[freebeard]

My 35ft R-license park model trailer came with hydraulic brakes in 1961 (the master cylinder levers off the hitch). I got two salvage axles with electric brakes that I intended to substitute, but now I'm concerned about affecting the resale value.

I also got a double-glazed 2x4ft skylight, but I put it in the slumlord's shop for the same reason. I curbed up the opening, but if I ever move I'll leave it covered with sheet polyethylene.