If the high beam headlight relay is not working, it may need to be replaced. To determine if replacement is needed, first measure the drop in voltage with a voltmeter. If a voltage drop is evident, replace the relay. All relays used should be equipped with heavy gauge wiring that ensures the voltage will not drop as the power is transmitted to the high beams. This wire should be stranded and earmarked for automotive applications only; never use household wire.Continue Reading
To test for a voltage drop, hook the positive lead for the voltmeter to the vehicle's positive battery terminal. Attach the negative lead to the positive terminal of the headlight in question. Record the voltage drop, and repeat on the other headlight. Add the two figures together to achieve the total voltage drop.
When choosing where to run the relay's wires, consider either the alternator output terminal or the positive post of the battery. For older cars with full-current ammeters, the alternator is the best choice, as it would keep a large current load away from the wiring system and prevent another voltage drop. Cars without full-current ammeters function well using either the alternator or the battery. When using the battery, however, be mindful of corrosion. Regularly clean the terminals, and spray them with a generous amount of terminal spray after connection.Learn more about Electricity