Make sure to follow the steps, Because it can save you a lot of time.

Print the left and right V-slut adapters. you will need to use supports. 

• 20% infill
• 2 Perimeters
• Tree support

Print the left and right angle makers.

• 20% infill
• 2 Perimeters
• Tree support

If you don't have metal T-nuts, you can print them. 

Install The Adapters And Place The Angle Makers using T-nuts and M5 screws.

Put an M5 screw in the angle maker's smaller hole and mount it on the adapter. Now it should rotate around 40 degrees.

For this, you may need to measure the back-to-back length of the angle makers when they're installed on the adapters (already on the printer obviously).

Open the light bar .stl in your slicer and correct the length of it (pay attention to only scale one axis, don't change the height and width). If your print bed is not big enough for printing it, you cant rotate it 45°, or if you dare, you can place it vertically.

Print the Switch Box

• 20% infill
• 2 Perimeters
• Normal support if you need it for bridging

Mount the switch and the barrel jack to the box and do the solderings. You know how to do it right?

but pay attention: you should disconnect the adaptors and the angle makers from the light bar before starting.

Put the light bar, angle makers, adaptors, and the switch box together and connect them to the V-slots.

It's done!