Hello, everyone...
My old Ford pickup has the blinking headlight problem, but it only happens after the brights have been on for a minute or two.. lows work fine. I've read a few threads where trucks were having this problem, and replacing the headlight switch and dimmer was the usual recommendation, but from what I've seen, these trucks were having troubles with the lows as well. So I'm wondering, would it be necessary to replace the headlight switch and the dimmer, or could I get by with just the dimmer? A friend of mine tells me that getting a new switch and dimmer for his truck cost him almost 50 bucks altogether. Is this about right, or did he just get ripped off? His is a '68 F100, mine's a '67 F100.

Thanks,
Ladd

 

you're running more voltage with the high-beams, so i'd imagine that's when the problem is more likely to show up- after everything gets good and hot.

the problem will probably slowly spread, and eventually hit the low beams as well.

 

I believe the head light relay carries most of the current. Silver thingy on the right inner fender.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

You guys have a headlight relay? Ladd, here’s what I would do. Replace the dimmer switch first, the contacts could be corroded and they don’t last forever. Then in about a month or so you can replace the headlight switch because it will eventually start blinking again. Now you have a new dimmer and switch and you won’t feel so ripped off.

Barry

 

First of all there is no headlight relay, although there should be see tech articles
Secondly the voltage is the same to the lights, 12 volts, whether selected high or low. The current is what is different, larger draw due to bigger filament for brighter lights. Current equals resistance divided by voltage, hence as voltage remains at 12 volts the higher the resistance the higher the current.
The lights are flashing because the circuit breaker in the headlight switch is tripping and resetting due to high current draw. This could be caused by many things, corroded wires, corroded contacts on the dimmer switch, corroded contacts on the headlight switch etc etc, all cause an increase in resistance. The usual culprit is the dimmer switch as it is exposed to all kinds of bad stuff being located on the cab floor
However over time all electrical contacts pit and burn as they arc from opening and closing. It really isn't an exact "this is what is wrong" science, unless of course you are skilled with an ammeter and can determine exactly where the high current draw is.
I wish I could say this is exactly what is wrong, but....... try bypassing the dimmer switch and running the lights on bright, if they flash it isn't the dimmer switch. If I remember correctly the power in to the dimmer switch is a yellow wire and the bright is a green wire. If you jump the wrong wires on the dimmer switch connector nothing bad will happen. You will only get bright dim or nothing.
Good luck.

Sparky

 

Sparky, would you send me an E to jowilker. I'd like to have you in my address book when I need a good answer for an electrical problem.

Do you have a suggestion for brightness control in the dash lights when you puill the light switch on. Sometines when I pull it on the dash is dark and I have to rotate the switch. Can something just be cleaned or something?

I suspect the horn relay was what he was referring to on the right side fender.

John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quite of night you can hear chevies rusting away.

 

yep...i never have managed to correctly wrap my head around voltage/current differences...

starting to think i should have taken more math in school...

 

Gee whiz John, you don’t like my short and concise answers? I can make them more complicated if you like with my EE background.

Your rheostat in the headlight switch is intermittent. You can try spraying some contact cleaner on the windings and wiper but it’s usually a short-term fix. These things just wear out over time, on mine the windings actually came out of the housing and shorted to the dash when I rotated it.

I suspected the horn relay too, just being gracious about it.

Barry

 

You guy's are surprisingly light on me for my mispeak.
I was indeed thinking(not) about the horm relay. As to the dash light dimness I also have a problem with that. They never seem bright enough. One would think that on full bright the rheostat would be shorted (bypassing the coil) and provide full brightness. Maybe something else is involved.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Beartracks, you are right. When the fader is on full brightness, the rheostat is bypassed by the wiper. John’s problem (at least with the dash lights ) is different, he has an intermittent, not dim lights.

The dim dash lights could be caused by the bulbs darkening due to age. This happens over time due to the filament oxidizing and leaving deposits on the inside of the glass envelope. They could also be dim because of corrosion in the connections from the fader to the light sockets and back to ground as Sparkey talked about. Also, just disassembling the instrument cluster and cleaning the bulbs and surfaces makes a difference.

As far as the misspeak, I have been wrong many a times and appreciate it when someone corrects me gently. After all, we’re just here to help and exchange ideas about our trucks and not to flame each other.

Barry

 

Barry, actually I have the problem on both of my trucks, and the dead one before. I didn't know if the switch could be cleaned or had to be replaced. I'm gonna stick a forsale sign on my blue truck in Carlisle, so I wont do anything until I get back if I still have it, and with the red truck, I'll just live with it.

Your answers have been excellent, what do you mean EE, you aint fooling nobody here. :-)

John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quite of night you can hear chevies rusting away.

 

<Your answers have been excellent>

Thank’s John, just pulling your leg a little.

< what do you mean EE, you ain’t fooling nobody here >

Maybe, but I fool 'em enough at work that they keep giving me a paycheck!

What happened to Ladd, did we scare him away?

Barry

 

Barry, I guess it's hard sometimes for them to figure us ol foolers. Just got to have a little fun every now and again.

John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quite of night you can hear chevies rusting away.

 

hey all,

I didn't get scared away... I've just been busy with work, and fixing a friend's R/C car... had to replace the clutch in it (yeah, it's alcohol/nitro powered) and work with some of the suspension stuff. Another friend of ours tore off the front right corner.. anyways.. I'll stop myself before I get way off topic here.. thanks for the ideas on the truck, I'll give 'em a shot as soon as I get the old beast running again, and if this thread is still around, I'll let ya know what I figger out.

Thanks,
Ladd