Headlight keeps burning out on one side only — electrical issue?

Few things to check: 1. **Are you touching the glass?** Oil from your fingers creates a hot spot on halogen bulbs. Always handle by the base or with a clean cloth. 2. **Check the connector** — a corroded or loose socket causes arcing, which overheats the bulb. Pull the connector and look for green/white corrosion or melted plastic. 3. **Voltage test** — with the headlight on, measure voltage at the socket. Should be 12.6-14.4V. Higher than 14.8V means your voltage regulator is pushing too much. 4. **Ground issue** — a bad ground can cause voltage spikes. The driver side ground on F-150s runs to the fender — check for rust. The [2005 F-150 wiring diagrams](/wiring/2005/Ford/F-150) show the headlight circuit and ground points. That'll help you trace it.

Almost guarantee it's the connector. The F-150 headlight sockets from that era are known for melting. You can buy a pigtail repair harness from any parts store for about $8. Cut the old one off and splice the new one in. Fixed mine permanently.

Also make sure both headlight housings are properly sealed. If moisture is getting into the driver side assembly, it'll kill bulbs fast. Crack the housing and check for condensation.