For the Sep event at Roebling, you need to have a FIA approved rain light on the back of your car in order to participate in a “Rain Race”. The light needs to be located in ~ the central 1/3rd of the rear of your car, not towards an outer corner. The light needs to be steady on. There’s useful info in both the MidAtl category and also the Electrical category.
On 1Jan19 your steady-on rainlight needs to be able to blink upon application of the brakes. Most rain lights come with 2 wires so it’s just a matter of wiring the blinky wire to your brake lights.
This is all covered in the SE Supps. SE Supplemental Regulations - Google Docs