I cannot remember which one I needed to complete the install but I believe it was number 8 in this diagram.
No. 8 is the tilt sensor.
snip
For instance right now I have a working taillight/brake light, working turn signals, but the constant-on feature of the turn signal lights is not working.
I never thought of that, I've only been wanting to add a brake light to my IS, not Supervalk and change my turn signals into running lights. But if I change the rear wires to a Std/Tourer wire harness, then I have one loose wire. Wont matter since I'm keeping my trunk, but it might be nice to swap out, and have extra running lights.