If you need to check the connection on the back of the gauge, remove both dash panels, by removing the 3 screws, and 2 push pins. To remove the push pins, push the center of them in, and then pull them out. To replace them, push center pin back so it is raised, stick it in the hole and push pin flush.
Once you remove the two dash panels there will be two hex bolts holding the guages down, remove these two bolts, then pull the gauges out. They will be tough to pull out, just wiggle them a bit. They are held with the 2 bolts and two pins pressed in rubber holes.
Once you pull it out, you will see a connector on the back of the gauge, make sure the big connector is seated properly.
Re-assemble.
If you still have the problem, you can remove the left fairing by removing all of the bolts and TWO push pins. One large one is located up top near the gas tank bolts. This one requires a flat head screw driver to pop loose. Pull the pin out.
The other push pin is located on the inside of the front wheel well. Kinda tough to see, but sitting on the bike and looking down through the hole as if to look at the ground or front wheel, they are down there. Pop those out.
It also helps to remove the seat and gas tank bolts to help free up the fairing. Once you get the left side off, you will see a wire with a connector going to your front sprocket cover. Make sure that is connected firmly.
If all of that checks out, you have some other problem, that might require someone with more technical skills.
It's not that hard to do what I've said. Give it a shot, you can't hurt anything...and if you get scared half way through, just put it back together.
Good luck.