This is what it looks like at night:
The first thing I did was use Eagle to design my PCB. The PCB needed to hold 4x LEDs with equal spacing between them so that the light spread nicely along the light bar.
My original design assumed I would use 3-pin LEDs, it turned out that I could not use those the way I wanted to so I fell back to using 2-pin LEDs, the PCB did not need any modification at all for this.
Here's the schematic I came up with:
The corresponding PCB design is:
Note that the 3-pin design is shown in the pictures, but it works just as well for 2-pin LEDs.
To get the PCB printed, I used OSH Park, was quite impressed with their service, you do have to wait a little bit, but it's cheap and the quality is very good.
So I waited about two weeks before my PCBs arrived.
The LEDs are bent into shape to line up with the PCB and pushed through.
All soldered in.
Next I had to design and 3D print some mounts for the PCB. The Octane had some pins that mounted the original light bar, so I worked around those and created two supports that look like this:
These fit nicely around the PCB:
...and onto the front of the Octane:
The HDD activity wire is connected and the lights seem to be working already:
The cover is back on, with flash on the camera it's easy to see where the LEDs are.
At night the light from the LEDs blends and lights up the whole bar.