I built this light for the bicycle rack on the rear of my car. It serves as an additional tail light and brake light.

Why: When I load the rack with several bikes, they often obscure the car's tail lights and upper brake light. This project helps make the car more visible, at day and at night.

Prereqs:
- This instructable assumes you have the electrical skills to wire trailer lights.
- This instructable assumes your car is already wired with connectors for trailer lights.

Caution: Please check your local laws to ensure this project is street-legal where you live.

Acknowledgement: This was not my idea. I saw one on the road. I was so impressed, I built my own.

Step 1: Parts and Assembly

Parts:
- Commercial trailer tail light assembly (I used an LED unit from Harbor Freight)
- Wire, shrink wrap, and connectors (from the trailer store)
- Wood, cable ties, string, goop glue, staples, paint (from the scap box)

Assembly:
- I cut a piece of wood to fit nicely on the bike rack.
- I attached the trailer light to the bottom of the wood two ways:
-- A glob of glue (Goop brand waterproof glue) between the light and wood
-- Two heavy cable ties (zip ties) around the light and wood
- I soldered a length of wire from the light to the trailer connectors.
- I stapled a length of string to each end of the wood.
- I painted it a visible color.

Step 2: Usage

Usage:
- Place bikes on the bike rack.
- Place light assembly on the rear of the bike rack. Tie strings rack securely.
- Route electrical cable to car's trailer connector, and plug them in.
- Test lights.

Design alternatives
- Instead of strings, use strips of velcro to attach the light to the bike rack.
- Instead of one trailer light, use two (one on each side) and wire them as turn signals.

Unrelated to this instructable:
Notice the tennis balls in the last photo. They help make the rack more visible in daytime. This is useful if ever I forget to lower the rack in a parking lot. It also softens the blow when I walk past the rack and slam into one of the arms.

Step 3: Finished

Results: It may be wishful thinking, but I believe drivers follow a little less closely, both in daytime and at night.

Enjoy your new light, especially when you head out in the wee hours of the morning to some distant randonneuring event.