But, to answer the original question posted here in 2001
,
if you install neon lights, or even have a neon light license plate frame, and these lights are lit while driving, you violate Michigan's Vehicle Code (see Chapter 6).
If installed on your vehicle (and this includes under car, license plate, and any interior lights such as dashboard neon lights), these neon lights MUST remain covered and unlit while on any Michigan roadway. See MCL 257.698.
Only white and amber lights are allowed in the front of the vehicle and only red and amber lights are allowed in the back of the vehicle. Only those lights that are required and permitted under the vehicle code are allowed, and no other colored lights of any kind are allowed to show on a vehicle (with emergency vehicle exceptions).
So, if you DO locate an auto shop in the Detroit area that will install neon lighting on the underside of your car, you will be able to enjoy and admire the lights while sitting in your garage.