Headlights go out then come back on

[youngbodean70F250]

When driving with my headlights on, my high beams will go out together, then come back on in a few seconds. It will keep doing this (it's great when it happens around corners) over and over. It never happens if I just use low beams, and no other lights (gauge or parking) are affected. I already changed my headlight switch, that didn't help. I do have extensive rust on the lower part of my radiator support (grounding issues?), but I dont think that's it. My wires all look intact, so is there some other relay or circuit breaker that's bad? Thanks for any help...

[crewdcab]

try replacing the dimmer switch. I've had it happen in multiple dents and bumps, and so far it's cured all of them.

[ForingaMex]

I would say 9 out of 10 that your headlight switch is bad. They have built-in circuit breaker and when they get old the start acting like that.

[fordman]

the ehadlight switch does have a circut breaker in it. and that is why the lights flash off and on when this happens. the only time i have had to replace a dimmer switch is when it has stuck and wont operate any more. but i have heard that it can cause problems too. because the wirign for the headlights go through that switch before reaching the headlights. one other thing to consider is the new headlight switch yo uput in may have been made in china and could be weak from the day it was made.

[youngbodean70F250]

You could be right, the new switch was probably made in CHINA, but I replaced it because of what the lights were doing, and they are doing exactly the same thing now. Aren't the dimmer and headlight switch part of the same unit anyway? Odds are it's probably something else, but I will start with a new headlight switch again, maybe Dennis Carpenter has a quality one. Wont find out until Spring, since the old boy is put away now for the impending Winter and salted roads. Thanks!

[CommrclDiver]

Not to insult your intelligence or anything but I'm sure you checked all your grounds and connections first before buying anything? My headlight switch was acting funny and I took it out and the contacts were corroded. A quick zip with a fine wire brush and it worked like new. Grounds on 39+ year old Vehicles are a good place to start for electrical problems. Make sure they are clean and free of rust. Again, a quick zip with a wire brush and good as new. Hope this helps.

[wildcard]

try replacing the dimmer switch. I've had it happen in multiple dents and bumps, and so far it's cured all of them.

I have to agree with crewcab. I would run down and get a new dimmer switch since you already have a new headlight switch. I even carry a spare dimmer switch since I drive a lot at night. And because when I've had that problem a dimmer usually fixes it. Plus they're a lot easier to change.

[grabberblue72]

I do have extensive rust on the lower part of my radiator support (grounding issues?), but I dont think that's it

your right, each headlight has its own ground. if it was a ground issue on the rad suport, it would most likely only be one headlight, not both. id focus on either the headlight switch or the dimmer switch. id definatly try changing the dimmer swith before changing the headlight switch again. the dimmer switches are bad for getting mosture in them.

[VirginiaCityFord]

quick question, I have all my outer light working but no dash lights. I changed the fuse but still the same. I'm thinking this runs through the light switch and my problem is there, any thoughts?

[Thunderfoot]

quick question, I have all my outer light working but no dash lights. I changed the fuse but still the same. I'm thinking this runs through the light switch and my problem is there, any thoughts?

Yes the dash lights are run from the light switch, it has a rheostat to control brightness by turning the knob. This rheostat can go bad.

[Thunderfoot]

youngbodean70F250 Did you replace the Headlights with newer High Wattage ones? If so then this is your problem as the circuit breaker in the light switch will not handle this extra load, you will need to do a headlight relay system like 390nut is doing. http://www.fordification.com/forum/view ... 11&t=36143

[Johnson]

I'm having the exact same problem with my 71 F-100, I figured it to be the headlight switch, just havn't gotten around to get one yet. The dimmer switch looks brand new, so I'm guessing the guy I bought this from was having issues as well. It's just not that big of deal for me because most of my driving in in town with low beams.


The link you posted with the upgraded wiring harness....is that for the newer lights, not just your old run of the mil halogen right?

[Thunderfoot]

The link you posted with the upgraded wiring harness....is that for the newer lights, not just your old run of the mil halogen right?

No, most halogen lights use more Amps then the light switch was designed for, they didn't have halogen lights when these trucks were made... Even using the stock lights, that harness upgrade will give you much brighter lights as the wire size and design of the wiring in our old trucks was not good and under rated.
The circuit breakers in the light switch do get week with age so replacing it may help, depending on the quality of the switch...

[1971ford]

do they ever flicker? like quick on-off-on ???
Or is it always a steady on for long time, steady off for a few seconds and back on?

If it flickers whats-so-ever, I would look over every inch of all the wiring and clean every plug... because it has to be a bad connection somewhere... but if it is steadily on/off then switch or dimmer
Not a whole lot to the headlight system (or any thing on these trucks), so its kinda weird when something is so tricky

[Hawkrod]

Lots of good info here, most of the ideas are right on. The most common problems are dimmer switch (they fail regularly as the contacts arc each time you press it), the grounds (if it is rusty or you messed with anything) and halogen lights are at the top of the list. Headlight switches don't fail as often as many think. They replace them and the problem goes away for a while but that is primarily because replacement light switches usually have a higher amperage circuit breaker because they are made to fit a lot of stuff (like cars with 4 lights instead of trucks with two) and so it hides the actual issue which is almost always resistance or later halogen lights that draw more power. The relay conversion will also hide the issue as it reduces the amount of power flowing in the main circuit. The reality is the stock switch and wiring is up to the job until it becomes compromised. I don't run a relay system and I have halogens in every truck I own and have never had an issue except for dimmer switches (keep in mind that I have had and worked on these trucks since back in the 70's so I do have a bit of experience! LOL). Hawkrod