I think I agree with you, I can find nothing specifically prohibiting the kind of light kit you are talking about. However, there is the possibility that they are trying to charge you with one of the following:§ 63-7-20. Use of blue and red lights and alternating flashing headlights
(1) It is unlawful for any person, other than a law enforcement officer on duty, to use or display blue lights on a motor vehicle as provided for in Section 63-7-19.
Perhaps the police officer who gave you the ticket thought the light was blue rather than purple.
§ 63-7-17. Use of spot lamps, auxiliary driving lamps, and signal lamps.
(1) Spot lamps. Any motor vehicle or motorcycle may be equipped with not to exceed one (1) spot lamp. Every lighted spot lamp shall be so aimed and used upon approaching another vehicle that no part of the beam will be directed into the eyes of the approaching driver. Spot lamps may not emit other than either a white or XXXXX XXXXXght.
Perhaps they consider these kits as spot lamps.
(2) Auxiliary driving lamps. Any motor vehicle may be equipped with not to exceed two (2) auxiliary driving lamps mounted on the front at a height not less than twelve (12) nor more than forty-two (42) inches above the level surface of which the vehicle stands. Every such auxiliary driving lamp or lamps shall meet the requirements and limitations set forth in subsection (3) of this section.
Maybe the kits are considered auxiliary driving lamps, and thus you can only have two mounted on the front.
(3) Signal lamps. Whenever a motor vehicle is equipped with a signal lamp to comply with the provisions of Section 63-3-709, the signal lamp shall be so constructed and located on the vehicle as to give a signal which shall be plainly visible in normal sunlight from a distance of one hundred (100) feet to the rear of the vehicle but shall not project a glaring or dazzling light.
Maybe they think these kits project a "glaring or dazzling light."
§ 63-7-41. Sale, use, etc., of lamps modifying original design or performance of vehicle.
No person shall have for sale, sell or offer for sale for use upon or as a part of the equipment of a motor vehicle, trailer or semitrailer or use upon any such vehicle any head lamp, auxiliary driving lamp, rear lamp, signal lamp or reflector which reflector is required hereunder, or parts of any of the foregoing, which tend to change the original design or performance, unless of a type which has been submitted to the department of public safety and approved by it.
No person shall have for sale, sell or offer for sale for use upon or as part of the equipment of a motor vehicle, trailer or semitrailer any lamp or device mentioned in this section which has been approved by the department unless such lamp or device bears thereon the trademark or name under which it is approved so as to be legible when installed.
No person shall use upon any motor vehicle, trailer or semitrailer any lamps mentioned in this section unless said lamps are mounted, adjusted and aimed in accordance with instructions of the department.
This last provisions seems to be a catchall provision meaning that unless the type of lamp is one specifically mentioned in § 63-7, it is prohibited.
So, perhaps you are being charged under one of these sections, or a combination of them.
Under these circumstances, I think you have two defenses:
1. A charge of "Improper Equipment" is too vague. You should argue that you are entitled to know precisely which section or sections of § 63-7 you are being charged with violating, and that the mere charge of "Improper Equipment" does not give you sufficient notice of the charge against you. You are entitled to proper notice of the charge against you so that you can prepare a defense.
2. You should argue that none of the provisions of § 63-7 specifically prohibits the types of lights you were using. And if these laws do not specifically prohibit the lights, then you are entitled to use them. For example if the police claim a violation of § 63-7-20 (no blue lights). You have to argue my lights are purple - the statute does not prohibit purple. And use similar arguments for the other sections above.
I think you have reasonable defenses. Good luck.