Q: My car is a 2005 Mercury Grand Marquis. My headlights will go off after driving half a mile. The directional and brake lights still work, and if I pull the directional lever toward me, the headlights will briefly come back on, while held.
A: Other than losing one's brakes, or encountering a stuck-open throttle, this has to be one of the creepiest situations one can encounter. At 70 mph, we travel 102 feet per second. Even with great reaction time and good brakes, you'd cover about two-thirds the length of a football field in darkness before bringing the car to a stop.
The Internet is abuzz about Grand Marquis, Crown Victorias and Town Cars of this vintage having this problem. In 2008, the National Highway Traffic Safety Administration investigated the issue. Ford reported 2,074 incidences of headlight failure during the first three years of vehicle operation, with 214 of these occurring while underway. Defective solder joints in the lighting control module, or LCM, were deemed the main culprit, but one must also consider that using higher-wattage aftermarket headlight bulbs could trigger a protective shutdown.
Renewal of the pricey LCM typically resolves the issue, after a test of three circuit paths. There are quite a few businesses rebuilding LCMs for $50 to$100 with a lifetime warranty; this would be my solution choice. Check eBay and local sources.
I called Lincoln Motor Co. owner services — Mercury is now defunct — and asked if a goodwill gesture or policy adjustment was in the works. I was told affected owners should contact them and that issues would be addressed on a case-by-case basis.
You mentioned the headlights returned as you pulled back on the turn signal lever. This is called flash-to-pass, and in these vehicles, headlight power is supplied via a different path than through the LCM. This could be a lifesaver, if one can remember to quickly execute the maneuver during an unexpected lights-out emergency.