early 99 headlights blink "ON"

[7.3early99F550]

I have done a search on my particular problem and have come up with nothing.

The problem: when I turn the headlight switch to the parking light position, all parking lights come on, but, about every 4 seconds the headlight bulb and gauge cluster lights flicker on for .1 of a second. You can stare right at the headlight bulb and see the filament flick on for that .1 second without it blinding you.

What I have done: checked all fuses and relays - good, replaced the headlight switch and multi function switch with known good ones, checked the harness for burnt terminals for the headlight switch.

It is not the alternator or regulator cause this happens with the engine running or not. Once you move the headlight switch to any other position, it works like it should.

I have run out of ideas. What are yours?

[7.3early99F550]

Just noticed something else with the head light switch. When I have the switch on the headlight run position first and move it back to the parking light position, the headlights dim to about have of their full on intensity for a few seconds then finally go out and start the blinking on again.

This is happening with two switches, the original F550 and a know good one I stole from my day driver F250.

Tail lights are not affected.

I am at wit's end.

[7.3early99F550]

anyone have any advise?

[7.3early99F550]

people are reading this post, please say something while you are here

[JSchuricht]

That's really weird. Your going to have to start tracing wires, I'm guessing something is shorting. A normal multimeter may not be fast enough to catch the temporary current so a test light may be better. Just start from one end and work to the other, isolating stuff as you go so you can pinpoint the section that is giving you issues.

[AMSOILdealer]

^^^ I agree. Are there any other devices running from the "hot lead/fuse block" that might be causing the backfeed. Also, does it have or had daytime running lights maybe another area to check? Just a few thoughts.

[ProOnThaSnow]

Check to see if your truck is equipped with daytime running lights - and see if the connector at the header panel/core support is fully connected or completely disconnected (If you dont want them on). It may have nothing to do with it, but if the connector was occasionally making a connection it could cause the symptoms you're seeing?