Truck/trailer light questions

[DKinWA]

This is actually kind of a truck and trailer question, but I thought I'd post my question here. Whoever wired my dump truck for a trailer before I bought it did something goofy I'd like to correct. When I plug in the trailer lights with the truck ignition on, the brake lights on the trailer come on. This happens even when the truck lights are off. As soon as I release the trailer brakes to move, the lights go out. Other than that, the lights work as they should.

When I look at the tractor protection valve (TPV), it's clear they rewired things and I'm reasonably sure they fouled up here. On the TPV, there's a brake light switch with two wires. There's also a second ?, with three wires attached to it. I'm not sure what this switch ?? is or how it should be wired. If anyone can provide any assistance, I'd greatly appreciate it. Thank you.

[RonG]

They are working as they should IMHO.
That is what I would expect of the brake lights on the trailer unless I am missing something here. Ron

[DKinWA]

Thanks for the reply Ron. You've confirmed my intuition they are working as they should. I've had a couple of folks tell me they're wrong and a recent inspection at the scales showed nothing wrong when they checked my lights. I've only been around the bigger trucks a few years and the folks telling me it's wired wrong have been around trucks a long time. I pretty much believed them and figured my logic was wrong along with the wiring :beatsme . I think I'll see what others have to say before I do anything with the wiring. Thanks

[Steve Frazier]

Some trucks are wired in this manner, others are not. There doesn't seem to be a standard as far as parking brakes go.

[triaxle]

Some power units , often Peterbilt and Mack do this brake lights on when tractor park valve is set others do not.
It is one of those things the FHSA will require uniformity on some day...