How to Troubleshoot Automotive Light Switches
Working lights are an important part of vehicle safety. Exterior lights allow you to see the road ahead and also alert drivers to your prese...
Working lights are an important part of vehicle safety. Exterior lights allow you to see the road ahead and also alert drivers to your presence and intentions. Interior lights allow you to see your map, what your kids are doing in the back seat and read your dashboard display. If any of these lights stop working, you could be in serious trouble. An accurate diagnosis can help you avoid a lot of headaches. The switches that control the lights are often the culprits. They should always be part of your diagnosis.
Instructions
- 1
Identify the problem system. Check all the fuses. Sometimes the power for the problem system is routed through an unexpected fuse. Remember to check for fuses in the engine bay.
2With the switch in the "Off" position, attach the negative lead of your multimeter to a chassis or engine ground. Check for voltage at the positive terminal with your other lead. Depending on the system, you should get a reading of 12 volts or 5 volts. Anything less or in between these readings indicates a problem before the switch. Fix this problem before proceeding.
3Check the ground side of your switch; the reading should be zero volts. Turn the switch to the "On" position. If the switch is a variable position switch, turn it to the full "On" position. Check the voltage reading again. It should read full voltage. If there is a voltage drop of more than .5 volts, there is a problem in your switch. If no voltage drop occurs, the switch is good. Check all terminals for loose connections. If connections are good, there is a problem after the switch that needs to be diagnosed.
4A voltage drop indicates high resistance in the switch. Remove the switch. Switch your multimeter to test for ohms. Check the result with factory specifications. Most switches should have almost zero resistance. If too much resistance is found, disassemble the switch. Use a wire brush to clean all terminals and contact points. Reassemble and retest the switch.
5Replace switch if resistance is still found.
