Voltage drop testing is a diagnostic strategy that uses a digital multimeter (DMM) or a similar tool to test actual circuit voltage and compare it with a desired circuit voltage.
If your headlight bulbs were installed at the same time, the life expectancy will be fairly similar. If one goes out, the other probably isn’t far behind. That’s reason enough to replace both. Deal with it once instead of twice!
You turn your ignition key and the engine fires up. It’s as simple as that, right? Actually, it’s quite a bit more complicated than it seems.