Lou, what era are you modeling? The four big eras of emergency lighting are:
Rotary - until the late 80's single or twin lights.
Full rotary (mechanical) light bar - late 70's to early 90's. Oblong shaped cross section of the light bar.
Strobe - 90's to about 2005 with a rectangular cross section.
LED's - 2005+ comes in multiple sizes and shapes. Retrofit kids available for earlier light bars.
There are special types like the NYPD V pattern lights meant to increase perpendicular visibility.
Fire trucks tend to be slow to adopt new lighting as the trucks have a 10-20 year service life. Police cars usually last 3-5 years. Ambulances about 5-7.
Each type of light bar has a very unique flash effects that can frame an era.
Most types can be modeled using Richmond Controls as previously stated.
https://evandesigns.com/collections/circuits Has a few solutions as well.
https://miniatronics.com/collections/light-bars These guys have been around a while.
http://circuitron.com/ Have some lighting controls that date to the early 90's.
While these will work, I suggest using a stationary DCC decoder. NCE has one designed for lighting and had a broad range of effects. I believe the ESU function decoders have a totally programable table.
Making the light bars is pretty difficult. Even the smallest LED'S are too large to make a scale light bar, especially LED prototypes. I would bury the driver LED's in the roof of the model and make an appropriate looking light bar out of clear styrene or sprue. The top of the light bar should have metal foil to keep the light from shining directly up - LED and Strobe bars have an aluminum skin on top.
For rotary light bars... Your guess is as good as mine. I have not seen a good simulation of one in HO, nevermind N.
