Corner Wrench: Trying to brighten your headlights? Maybe it’s your switch

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Running power from the battery harness to the lights, through narrow gauge wires via a circuitous route with plenty of small contacts can bring enough of a voltage drop to substantially affect headlamp output. On older vehicles there’s less opportunity to improve output without moving up to a more powerful bulb, as they don’t easily lend themselves to safe LED lamp conversions. When the voltage drops low enough at the contact point with the bulbs, their output can drop exponentially. So, for example, if a bulb is rated at 1,000 lumens when 12.8 volts is supplied, it can lose almost half of its power when the voltage dropped to 10.5 volts. So a good place to start is at the back of the lamp bulbs with a multimeter to see what you’re working with.

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If you’ve got even a 1 volt drop, you can be losing 30% of lamp output. Headlamp relay kits are readily available in just about any auto parts store. For as low as $50 you can often find complete kits with protected wiring, bulb connectors, separate high-beam low-beam relays, and inline fuse protection. The main benefit to a relay conversion is the shorter, more direct route from the relay to the lamps. Kit instructions will suggest locating the relays as close to one of the lamps as possible (usually at the rear of the radiator support or front corner of the engine bay). In most cases the original wiring that ran from the high-beam/low-beam switch to the lamps can be used to power the relays, as these units take very little energy to work.

If your kit doesn’t come with one, get a split loom protector sleeve to keep the job neat and secure. Often the radiator support has a cover or top rail to secure the harness as it makes its way from one side of the front to the other. If you don’t remove any existing wiring, make sure you protect those circuits from corrosion or moisture damage.