I'm planning on fixing it the "right way", but for my own edification, why is splicing 12V to the amp sense line a Very Bad Thing? I must be missing something here - all I'd be doing is powering the tuner (and the extra external serial) off of 12V, as the rest of the net is disconnected from everything else. Basically, I won't use it as Amp Sense, I'll use it as "tuner power".

edit: Oh, never mind, yellow will be hot even if the car is off. Duh.