Have an assistant hold the handle bars of the bike with one hand to keep it steady. Have them use their other hand to lift the seat to raise the rear wheel of the bicycle off of the ground.
Ask your second assistant to spin the bike pedals to turn the rear wheel. Have them hold the frame of the bicycle to help stabilize it during the testing process.
Grasp the two probes of your bulb-type voltage tester keeping one in each of your hands. Hold the tip of one probe against the electrical lead on the back of the generator (also called the dynamo) located next to the rear wheel of the bike. Touch the remaining probe to the other lead on the generator. Look at the light on your tester to see if it lights up.
Use your tester to check for electrical flow at the leads on the back of the light assembly in the front of the bike. Be sure your assistants are holding the bicycle steady and keeping the rear wheel spinning throughout the testing process.
Have your assistants stop spinning the pedals and hold the bike steady. Slide the tip of your flat screwdriver to pry the cover off the light assembly. Pull the bulb free. Have your assistants spin the pedals to resume the electrical field through the circuit. Test the leads where the bulb is normally mounted.
Replace the generator if the first test does not light up your tester. Replace the wires if the test at the rear of the light assembly fails. Replace the light bulb if the final test does not light up the bulb in your tester.
Things You Will Need
- Simple, bulb-type voltage tester
- Small flat screwdriver
- Work gloves
- Safety glasses
- Before you begin testing your bicycle lights, look at the dynamo (generator) to be sure the flywheel is touching the appropriate part of the rear tire as recommended by the manufacturer.
- Some types of dynamo-driven bicycle lights may require you to open the rear casing on the light to reach the ends of the wires for testing. Your screwdriver will usually get you into this part of the casing. If not, be sure to use the appropriate tool for the fastener holding the assembly together to avoid damaging it and disabling the lights.