"Dear Trooper Ness: I am a member of the ILARNG and work as a security guard for the same. We recently acquired a police light bar for use on our emergency response vehicle on post. This has touched off a debate. One of our sergeants claims that there is a provision in IL statutes concerning the fact that the red light side must be on the left of the vehicle and that certain colors of lights are given to certain population areas. i.e., all red for cities under 150,000 pop. Are either of these true? I have looked all through the Motor Vehicle Code (I am a law student) and the ILCS and found nothing."
Randy, the Illinois Compiled Statues addresses emergency vehicle lighting in 625 ILCS 5/12-215. What lighting is allowed depends on the type of emergency vehicle. For instance with respect to Police Squad cars: Red lights are allowed on all state and local municipality Police vehicles, Blue lights are only allowed on these vehicles in combination with Red lights. The only exception is for Police Squad cars in cities with a population of 500,000 or more. (Chicago)
To answer your specific question, the law does not designate which side the red or blue lights have to be on, they can be on in any combination. In fact some light bars mix the colors on both sides. That said, as an unwritten rule, the red lights are usually on the driver's left side of the squad, and blue on the right.
My only other concern is the status of your squad car. It must be designated as a Law Enforcement Vehicle (obviously in the case of the Illinois National Guard a Federal or State authority). Your unit would probably have to be designated as Military Police for this purpose. Otherwise, the vehicle code only allows regular Security vehicles to display Amber (yellow) lighting. Hope that information is helpful.