It doesn't make the radio CD quality. It's still radio, HD= Hybrid Digital, not High Def. After the digital locks on (takes a few seconds), it might be a LITTLE crisper sounding, but nothing major unless you had a really high end audio system.
I'm pretty sure there's an actual (ABS) light that comes on. On my 93 T Bird I had, whenever I spun the tires to much on ice/snow, it would kick on the ABS light, it would just get reset by turning it off and on again. Could just be a goofy computer mix up.
Nothing major... yet. PI manifold, Magnapacks, high flow plenum, C Springs, M/M CC plates, M/M FLSFC's, M/M LCA's, MM clutch clutch quadrant kit, Tokico HP's, Bullitt front brakes, Tri-ax,... PI cams in the garage....