Seriously, did you look at the TEWD link I put up?
There is no relay. Power goes from the battery to the STOP fuse, from there, it goes to the brake switch, and on to the failure sensor module, where it gets passed on to the lights. It should take a very short time to diagnose this.
I'm also not a fan of deleting the failure sensor box. I like having something tell me when I've got tail lights out, since it's hard to see for myself, and the last thing that I want is an excuse for the local constabulary to pull me over for a chat.
First off, pull the STOP fuse. If the brake lights go off, then at least you know that they're getting power through the correct circuit.
If you're getting power to the brake lights when you don't want it, check first that the tail light failure module isn't at fault. Disconnect it, and check for +12V at the green/white wire (Pin 7) at the failure box. If there is +12V on that line, then the failure module is NOT the problem, since the brake lights SHOULD be on when that line has power.
Next check that you aren't getting power between the switch and the failure sensor. Unplug the switch at the brake pedal. (It's a fairly simple switch, and not too difficult to get access to.) If you unplug the switch, and the brake lights stay on, then you've mucked up the wiring somewhere and bypassed the brake switch. If they go off, then troubleshoot the switch. It's also a pretty simple thing. If the pedal is up, it depresses a plunger, opening the switch. Pressing the pedal allows the switch to close. In my old Neon, I had a problem where the switch mount was a bit loose, so the brake lights would come on sometimes at random. I fixed it with a zip tie (it was a Neon, after all) and it never gave me a problem again.
So, your potential problem points:
Bypass of brake light switch.
Mechanical failure of brake light switch, possibly mount, possibly the part of the brake pedal bar that presses the switch.
Tail lamp failure sensor. (Unlikely, IMO.)