i've had similar issues with 3-way color/dimmable arch lights on the 45. they would fail to turn off, not dim, and also get out of synch..1 red, 2 blue, etc. On my 45, there is a small panel that connects to all of the arch lights, and terminates the cables from the dimmer switch on the panel. you could check your wiring diagrams to see if you are supposed to have one too, but if they dim, i assume it's there. on the 45, it was above the aft most arch light, starboard side. that panel could be the issue, but i found that my arch lights had some horrible connections that weren't water tight. i presume this was something the previous owner hacked into, because i've never seen connections like that from the factory. i suspect that i had water intrusion in one or more of the light connections, and that threw everything out of whack. i re-wired all of the connections while using shrink tubing everywhere and haven't had any issues since.
good luck with this one...
twarble