[Jon Stratis]

Try it without the RSL plugged into the Sidecar. In fact, try it with nothing plugged into the sidecar except for power and the cRio.

Are all 3 LED's (5V, 6V, BAT) brightly lit on the Sidecar?

Try replacing the sidecar.

If all of that fails... I don't know what advice to give you. I had a team at one of my regionals have an issue getting a battery readout on the driver station. They replaced all the hardware involved, tried it with multiple combinations of old and new hardware, and nothing worked. When we took the analog module+breakout to another robot and plugged it in there, it worked instantly. We never could figure out why it wouldn't give us a readout, but we ended up just having them play as they were. In the absolute worst case, having that light not working properly doesn't stop the rest of your robot from working, and since we're out of the competition season you won't have a Robot Inspector telling you to fix it before competing. Just make sure you take some extra safety precautions so everyone in the area knows the robot is running when you turn it on/enable it!