Tonight I drove my new (to me) 1967 F-100....first time I used the headlights. Pick up my boxsprings and saw the alternator light flicker when I turned off the engine and when I started it. Ok.........now it's dark and I'm driving home...I have no dash light......country road I'm on- no street lights....I'm using the high beams and switch to low when a car comes......I pull over to let some cars pass me ...I rev up the engine while parked and the headlights go bright and dim somewhat at idle........I do the last leg home.......now my road is a even smaller country road..... lots of turns and ups and downs.....I go around a corner and the headlights cut off....I can't see a thing....no road or ditch...no dash lights....I stop...brakelights look to be out also.....hope a car doesn't come around the curve.....I'm *real* scared...luckily no cars on the road....I stop and switch gears......lights go back on........I drive and they cut off again....I started to pull into a driveway to get off the road and they come back on.....I'm close to home so I start driving hoping they stay on......they go off again then come back on......I was glad to see my driveway!!!! Last time I drive her at night.....I park and turn the car off unload the boxsprings.....try starting the car and it doesn't turn over....finally turns over (I think I flooded it) and let it run for 10 minutes......I park it and hope it starts tomorrow........

I'm still scared........

 

Might be the headlight switch itself needs to be replaced it was in a post no to long ago that it flickers when its about to go. Or track down all the headlight wiring for breaks or bad connections. I'm not to big on electrical stuff so mabey someone else will pick up where I left off.

 

Replace the switch. They'll start acting like that when they're about to go out.

The same thing happened to me at about 1 AM on a highway near Dimebox, TX. I had just let a truck pass when my lights started flashing on and off. It must have scared the hell out of him. It kind of scared me as well; I didn't want him thinking that I was holding somebody hostage or anything.

 

I had a similar problem, lights go brighter with rpms and go dim at idle, engine runs fine, but the electrics are wiggin'. Bought a new alt., voltage regulator, and some new battery cables(not that the battery cables had anything to do with it, just figured they would look nice with the new engine). anyway, that fixed it and the whole bunch cost ma less than $80. hope this helps.

Oh my lights do still freak on me sometimes because the switches(lights and ignition) need to be replaced, wich may be the same thing you are getting. None the less, a 13 year old alt. and 35year old volt. reg., time to replace before I got stranded.

 

Wow- great to know that this has happened to someone else...not that I'm glad it did but you learn from other people's case histories.... guy I bought it from didn't drive at night so probably didn't need the lights. I have to work on getting the dash illuminated so I'll start reading up on the light switch and alternator.

Thank you 460 Crew, bigric and Ranger240 for your responses!

Be interested to see if this happened to anyone else?

 

I've had this problem on my 67. It turned out to be one of the trailer wires grounding on the bumper. The headlight switch would get real hot.
The problem with my 71 was running 80/100 watt halogen headlights. I installed relays and took care of the problems.
Turn on your headlights for about 10-15 minutes and place your hand on the headlight switch (under the dash) and see if it gets hot. Maybe the connection maybe loose.

 

my truck has always done that and still does...i was driving at night towing a trailer (was heading home from camping) and wham off...on...off...off...on...then nothing. good thing i had my trusty 1.5 million candle power light, also a good thing that my cig lighter still worked at the time. it was the switch as has been mentioned before...but i still love how my lights get brighter when i rev it...it really adds to the fear factor of the ricers when when they not only hear and feel my truck turn out those horses as i smoke them off the road...my friend calls it the "monster effect" its kinda like those big monsters in movies with the glowing eyes that get brighter when their mad

Signed,
The Don

 

I would also look at the bright/dim switch on the floor. They are notorious for NOT making connection. It will click like it works, but nothing will happen. I've lost headlights before when I tried to go from HI to LO beams....kick the switch and have them work again. Cheap/easy fix.

Headlight switch is also known for making dark driving. If the contacts are bad, or got hot it will cause lights to fail/flicker. If dash lights dont work already, then I'd say its a good place to start. Sounds like the resistor windings for dimming are already gone.

Larry

 

Talked to a mechanic who's worked on Ford trucks for 20+ years- says that it sounds like the headlight switch is bad (like all of you!) that was a weak point in the truck that year- if you're patient they come back on eventually.....I have a 67 F-100 for parts and he said don't bother taking the switch out of that- same thing will happen...he also said the alternators are historically strong and use a voltmeter to determine whether it may be a culprit....

Freightrain- I was switching from low to high beams a number of times before the lights went out....in my panic I thought I pushed the button and they came back on- but I don't remember- too concerned about not running off the road. All gauges work in the dash- also got that little blue light showing high beams- that lit up......but no other dash lights.

 

All true!

The headlight switch has thermal circuit breakers that automatically trip off and then back on. Over time they get weaker (thermal resistance through contacts and breaker) and heat up with normal loads.

The dimmer switch contacts just corrode from being on the floorboard.

Barry

 

Could also be a bad relay, I had that problem in my 79 Bronco...must be a Ford thing anyway I replaced the dimmer switch first and it still did it. After I replaced a couple relays the problem went away...The lights were also much brighter.

 

There's no relays for the lights.

 

Same thing happened to me in a 70 F-100, 71 F-100, and 68 Chevy Nova. All three times, it was the dimmer switch.

 

Same thing happened to me in a 70 F-100, 71 F-100, and 68 Chevy Nova. All three times, it was the dimmer switch.

 

ok must be different than the 79's