I searched but couldn't find an answer so here I go. A while back I was driving in the dark when my headlights cut out, no other lights just those two. It was intermittent and no rhyme or reason. I searched around for bad connections and fixed a few. Fast forward to the other night and they cut out again, this time a bit longer and then my instrument cluster lights cut out. They were in and out for the ride home where I parked it. Tonight I turned the lights on and everything works.

Any advise on possible problem areas? Starting point? I want to avoid getting flustered so before I re wire the truck I come to the experts. Thanks.

 

circuit breaker on headlight switch could be getting wreak . may need new headlight switch or something is overloading it.

 

have you added any fog lights ect that could be drawing to much current?

 

My only experience with lights cutting out was when I was driving my '75 F150 about 10 years ago. I had the headlights on low and they started to flicker a little then went out. Scary you know what when you're doing 45 and it's pitch black out. First thing I did was click on the high beams and they worked perfect. I pulled off the road and clicked the low beams and high beams a few times and they seemed fine. I decided to go home with the lows on and it did it again so I left the high beams on until I got home. Next day I bought a new headlight dimmer switch and put it on. Never had another problem with it. It made sense though, the dimmer switch is on the floor and gets stepped on with wet and dirty shoes over the years it's bound to get corroded and worn out eventually.

 

I haven't added anything to the headlight circuit. PO might have at one point, typical 79 ford, wires to nowhere haha. I've been cleaning it up slowly when I make the time. The dimmer switch is new. Maybe I'll pick up another one and a headlight switch as well.

Come to think of it, the PO swapped to h4 headlights, maybe related?

 

Anything's possible I guess. I swapped in some h4 LED headlights and I've had no problems. I would check all your connections and wires going from the headlights back into the dash. On the two trucks I have (75 and 77) there's a plug if you trace the harness back from the headlights a few feet and then that runs back to the firewall I believe. You could check that plug to see if it's corroded or plugged in tight.

 

If your windshield seal leaks, it drips on or near the dimmer switch. Not good. I would have to fuss with the switch if I accidentally bumped it. The replacement wasn't exact, the terminals were horizontal or vertical so I either pulled the terminals out of the plug or crimped new ones on and skipped the molded plug part.

Michael

 

These old trucks have lots of corrosion in the grounds, cables and connections by now, or paint, if restored. And the manufacturers used the smallest gauge wire they thought they could get away with. Some trucks had that problem even when new. High resistance means switches get hot because the current is being lost. Headlights don't use fuses, they use an internal breaker, for safety reasons, as you discovered.

You can install headlight relays to take the load off the headlight switch - and get brighter headlights too - but cleaning up the circuit path and ground points should at least eliminate surprises like that. Any electrical connection needs to be clean and shiny, and tight, or it will eventually fail. You may need a new switch by now, the breakers get weak eventually. Try to find an older Motorcraft switch, import electrical parts are not always of good quality.

 

Mine did that a few times. It was the dimmer switch.

 

Yeah, anything that adds more load, whether it's from higher power bulbs, or just old tired wiring and ground contacts, the circuit breaker will definitely give you something to freak out about when you're driving down that nice dark country road!
Might even make you see stars!

And yes, your new H4's could definitely have caused it. Very likely in fact, from just pushing your old switch over it's threshold.
The original low-beams on some of the trucks were only 45watts. Not sure when they raised the limit to 55watts, but the H4's start at that level and go up from there, depending on which ones you got.
Sounds like it was just your switch's time...
In my case I probably hastened the fall of the switch by having so much fun with my new super bright high-beams whenever I could. Just finally pushed the old circuit breaker too far one night.

In a pinch, if it ever happens again and you need to get back on the road safely, get under the hood and unplug one of the headlights. You'll be one-eyed, but at least the remaining light, at roughly half the load on the switch, should stay on for much longer before it happens again. At least it might get you home.

But the real cure for overloaded switches and dimmer-than-they-should-be headlights (besides a new wiring harness) is a headlight harness using relays. Takes the load off of the dash switch by running power over a more direct route from the battery to the lights.
I'm pretty sure there are discussions about it on the forum all over the place. I think I just saw one recently in fact.
I made my own harness, but there are kits around if you're not comfortable doing it yourself.
We have a very reasonably priced (Chinese of course) one that's longer than needed for the Early Broncos, but haven't tried it on a full-size yet. The more expensive USA made one we have is always too short for clean routing unfortunately. So I always prefer selling the cheap one instead. It's a shame, but true.
Likely even that one is not really long enough for a full-size though, so make sure you get one specifically designed for big trucks so you can route the wiring cleanly.

Oh, and if you do go with a relay setup, which I think you should, given the number of people that have upgraded and love it, it might actually let you pass on changing your old light switch.
The one in my truck started flashing on my over 20 years ago. After the relays fixed the issue, I'm still running that same old (original) switch from '71.

Paul

 

Thanks for all the reply. I ordered a new dimmer switch and headlight switch. I figured I'd start simple and move on from there, besides I don't mind having spare parts. The relay is definitely something I'm going to look at doing in the near future. Thanks again.

 

I added higher power bulbs and ran into the same random lights out issue. I installed a headlight relay that took the load off of the headlight switch and that fixed my issue and brightened my lights too. Went back later to replace the headlight switch since the relays were just a band-aid to the real issue.

 

I had the same thing happen in the yellow truck. Quick and easy fix is to install a "relay-based headlight harness". You can get them from Bronco Graveyard and LMC for under $30.

Basically, what's happening, is all the current, for all the lights, travels up a small gauge wire to the headlight switch. The power then goes to the dimmer and headlights. As the switch and wires become old and corroded, they need to pull more amps to deliver the same power. More amps overheats the wires and the switch. When the switch overheats, the built-in circuit breaker cuts the headlights.

The relay harness comes right off the battery, and your existing headlight wire only needs to throw a relay to turn the lights on. The new harness delivers more power, safely, and gives you brighter lights.

But while you're in there, make sure all your grounds are good.

https://www.ford-trucks.com/forums/1...t-harness.html