The Arctic Cat Firecats have a simple mechanical fuel level gauge mounting in the top of the fuel tank. The problem is that when you are driving around at night, there is no illumination on the gauge so it can't be seen. After nearly running out of fuel one night, I decided I needed to come up with something better than carrying a flashlight in my pocket to check the fuel level.
I managed to find some high intensity green LEDs that I thought would go with Arctic Cat Green colour scheme. I made a small metal holder that holds one LED and directs it onto the gauge face. The holder mounts to the plastic piece where the steering column comes through.
In order to get power, I tapped into one of the 'accessory' wires under the hood. The power from the accessory wire is AC. I ended up putting together a small rectifier and regulator circuit to convert it to about 5v DC based off of this schematic. That probably was not absolutely necessary since the LED would have just allowed current to pass on one side of the AC cycle and prevented it on the other side. Throw in a capacitor, and it probably would have ended up with the same effect without noticable flicker.
A current limiting resistor was used to prevent the LED from being cooked.
This should give you some idea of what the final result looked like. The photo has a lot of glare due to my less than ideal photo taking skills, but in acutal use, the gauge is now easily readable without having to drive under a streetlight at night.