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Here is a nothre puzzle on me 66 F250. When I turn the headlights on, they stay lit for about 5 seconds, then start blinking, and then go out. If I shut them off, the same pattern occurs again.
I put a new switch in a couple of years ago and didn't have a problem until now.
Checked the wires to the lights. There is no difference if I move any of the wires, the lights flash even when it is sitting still. I will check the grounds and see what happens.
Updates: Check the all the grounds I could find (some loose) but no improvement. When I turn on the dome light, and parking lights there is no problem. It is only when I turn the headlights on that they start flashing.
Has anybody gone through a similar issue? I know electrical issues can be tricky.
I figured the same thing and went down to the parts place and got a new dimmer switch. But after the intallation, the lights would do the same thing on the high beams. After running out of ideas, I tried playing with the light switch a little more. I found out that I could slide it into a position just before it maxed out and the high beams stay on without flickering!? I am thinking the switch may be the problem even though I replaced it 2 years ago. Some of these aftermarket parts just don't last very long!
There is a metal clip/spring tang inside the light switch that can affect what you are describing. Don't confuse it with the one you can see outside the housing that is a rheostat for the interior light brightness. If you replace the light switch it will go away. Or you can drill out the 4 solid rivets (only remove the bucking) and pull the switch apart and clean the contacts. I simply replaced the rivets for screws on mine so I can clean it out when I need to. You can still get the switch from most part places. Some better then others in quality though.
Didn't think you could acutally take them apart like that. I did check and the switches are available at most auto parts stores. Seems like a similar design has been used on a number of vehicles for a long time. Prices are a little strange...I found a web based site that sells them for under 3 bucks? It seems like most range from about $16 to $24 around here.
I will probably by a new one for a quick fix, and then open the old one as you describe.