My 2002 F150 Supercrew headlights have begun to flicker at approximately 30-45 second intervals. I haven't noticed if any of the interior lights also flicker or if the volt meter changes when it occurs. The alternator appears to be charging since I checked it while running. Any advice?

 

But it prob on it's way out..... how old are the batteries? Put a voltmeter on the Alt output to see if it's steady or varying.

 

I'm pretty sure the battery is old and I will try to check the alternator output if there is a simple way to do it. Suggestions?

 

Just put a good meter across the battery with the engine running. You should have around 14 volts on the battery.

Keep an eye on the dash voltmeter when you have the flickering problem. That will narrow it down to a system voltage problem, or a problem with the headlight circuit.

 

The battery charge reads 14.5v when the engine is running so the alternator must be ok. I checked the volt guage when the lights flicker and did not notice ANY drop/change when the flicker occurs. Could it be the aftermarket fog lights or a ground strap problem? The fog lights have never caused a problem in the 5+ years they have been installed?

 

Disconnect the foglights temporarily and see if the problem goes away. If it does, it may simply be a poor ground to the foglights.

 

I let the truck sit for a week and the battery showed 11.7 volts. I decided to go ahead and get a new battery since this is the original (Motorcraft) thinking it may the problem. It wasn't.

The next time I drive the truck I will disconnect the fog lights to see if that is the problem.

 

Disconnected the fog lights and the flicker still occurs.

 

In older Fords the culprit was the headlight switch assembly.
It had a circuit breaker that would cause a flicker.

I'll have to see if that is still a possibility.

http://www.35thatr.org/Tips/HeadlightsFlicker.htm

 

I believe that I may have solved my flicker issue. I was also having an issue with the ABS light occasionally coming on. I finally found that the right front ABS sensor was touching the exhaust manifold and melting/possibly shorting. I replaced it and my ABS problem disappeared. Now that I have driven it at night the flickering also seems to have cleared up.