'04 P71 - rear deck lights

Hi - I have an 04 CV P71. I want to add amber LED turn signals and red LED brake lights on the rear deck. I know I can tap into the front directional signals to power the turn signals, but I'm trying to figure out the best way to deal with the brake lights. I read in the "CVPI Modifier's Manual" from Ford that you should not add anything to the brake light circuitry becausee it is also part of a system that will affect the transmission. But I read elsewhere that it is OK to tap into the brake light wiring after it enters the trunk, such as to add light wiring for a trailer. Does anyone out there have a definitive answer to this? I'd like to tap into the wiring for the "third" brake light, but I don't want to mess up other systems in the process.
Thanks

I once was also looking for LEDs for my park/brake lights. I don't remember where or which website it was, but there is a company that makes a "control pack" to add into the circuit to prevent oddities from happening with the other systems. I'm trying to remember, but I think the individual bulbs were like $9 USD apiece and the "control pack", which was a small boxed circuit board that was plugged inline was like $29 USD. (The "control pack" plugged in before the light circuit got to the rear lights, so it was a plug_n_play setup, kind of like the setup that Uhaul sells for trailer lights..) I think you had no problems with the front park or turn signal lights at all. It was just the rear park and brake lights that was the problem.

I wish I could remember which website it was. I guess I better start searching again.