This is a part that I modeled to replace the end caps on a common 13" light bar to mount to the top rails of the Ender 3. 

The benefits of using this particular light bar is that it has a built-in switch, and voltage regulator for 24V. This allows it to be wired directly to the extra outputs on the stock Ender 3 power supply, and turn on whenever the printer has power.

Here is the link to a 2 pack of these light bars from Amazon: 
https://www.amazon.com/CZC-AUTO-Interior-Motorhome-Trailer/dp/B08T8VSV4W/ref=sr_1_8?crid=37NMFUSTKT3T1

These are safe to wire directly to the Ender 3, though you will need some extra wire and either solder or a few crimp connectors. It is a really simple install, and I can provide more pictures if there are any questions.

This can be printed with no supports. The holes are at 45 degrees for an easy print. 

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