When I got my IS back in '08, didn't know about the backoff mod setup. Also didn't know that every IS didn't have a taillight on the finder. The PO had put them on. The taillight on the finder and the brake lights in the trunk flash opposite to each other.
I’ve got some amber/red switchback LEDs on order for the rear blinkers, too. I’ll run them without the running light mode similar to stock. They’ll blink Amber for turn signal and steady red for brakes. They were cheap enough that I’m willing to experiment with the factory Amber lens in place. If I don’t like the brake light mode then I’ll just disconnect that wiring and have an LED turn signal. Already planning to solder a diode into the turn signal indicator bulb up front.