Usage of neon underglow lighting is governed by Massachusetts Registry of Motor Vehicles, Section 22.07: Mounting and Display of other Aftermarket Lighting.
Is neon underglow legal in Massachusetts?
Massachusetts law specifically forbids the usage of after-market lighting and neon underglow. Therefore it’s our conclusion that in Massachusetts neon underglow is illegal.
Furthermore MA laws prohibit the use of blue lights, and flashing lights, without special permits.
By rigorous Massachusetts laws even installing underbody glow is illegal, so even if you intend to use it only on private property rather than while driving, do so at your own risk.
Massachusetts vehicle lighting laws
Below are all relevant excerpts from Massachusetts Vehicle Code that limit, restrict or allow certain aftermarket lights to be installed on vehicles.
Massachusetts Registry of Motor Vehicles Section 22.07: Mounting and Display of other Aftermarket Lighting
No person shall mount or display any lighting device which does not comply with Federal Motor Vehicle Safety Regulations, 49 CFR Part 571, unless specifically allowed by M.G.L. c. 90, §7. Such prohibited devices shall include, but not be limited to, neon undercarriage lighting.
In addition to the above, Massachusetts General Laws (see: Chapter 90) also include the following restrictions on vehicle lighting:
Section 7 – Brakes, braking systems, mufflers, horns, lights, audible warning systems, and other equipment
[...] No motor vehicle so operated shall mount or display a flashing, rotating or oscillating light in any direction except pursuant to section seven E of this chapter; provided, however, that this shall not apply to the use of rear directional signals nor to the proper use of vehicle hazard warning signals as provided for by this section. [...]
Every motor vehicle registered in the commonwealth shall be equipped with a device to permit the front and rear directional signals to flash simultaneously, said device to be operated only when the vehicle is disabled or stopped in the event of emergency on or at the side of any way.
Section 7E – Display of red or blue lights on vehicles
No motor vehicle operated pursuant to section seven other than fire apparatus, ambulances, vehicles specified in subsection (b) of section 50 of chapter 33, school buses, vehicles specified in section seven D used for transporting school children, and vehicles specified in section seven I shall mount or display a flashing, rotating or oscillating red light in any direction [...]
No motor vehicle, as hereinbefore provided, requiring a permit from the registrar, shall mount or display a blue light on such vehicle until proper application has been made
Violation of section 7E of Massachusetts General Laws carries a fine of not less than $100 and no more than $300.