New Moto Guzzi Door Mats Available Now
What I do....Get a normal incandescent taillight bulb. Add long wires and clips. Add some heat shrink. Carry with you is a trouble light and debug tool. Most of the time you really don't need to know if it is 12.4 volts or 12.8 volts. And being incandescent you don't care about getting the wires backwards.