Just yesterday morning as I was leaving for work. I noticed that my headlights didn't work when I turned them on. After checking to make sure that the fuse had not blown and after about 15 minutes of total frustration, trying unsuccessfully to locate the problem with a flashlight in the dark. Without much of an expectation of getting any response, I finally decided to try stepping on the highbeam/dimmer switch on the floorboard. Much to my surprise & relief, my highbeam lights came on just in time for me to make it to work without being late.

Although it's been quite awhile, I seem to remember having to replace one of my headlights in the past because the low beam filiment had gone out. However, this time it's both sides that don't work. Considering that it's very unlikely that the low beam filiments on both headlights have gone bad at the very same time and since the fuse is stiil good. I also doubt very much that it could be a wiring problem. So, now I'm kind of stuck on where I should look next to try to solve this problem. I'm thinking maybe the headlight switch itself or possibly even the highbeam/dimmer button on the floor?

Even though I do have a digital voltmeter, as well as the ability to use it. What I don't have is a wiring diagram with the color code of the wires to check before deciding on what needs to be repaired or replaced.

So, once again "as always" here I am, begging for help from the guys with the most experience, at the best place that I know of, to find the best answers possible for any problem or concern that I may ever have about my truck.

Q: Has anyone out there had a similar problem?
If so, What was the cause & solution?

Q: Does anyone have the wiring color code for the low beam "output" side of the headlight & dimmer switches?

And . . . "AS ALWAYS" I'm very sure that the responses I recieve to this inquiry. Will no doubt, lead me to successfully resolving this problem without the need of draining my wallet dry!

Because, as everyone who own's one of these old trucks already knows. That position has already been (and I hate to say it) "filled" by the gas pumps!

Thanks Guys! You're the Greatest!

I love this place!

Larry Bailey a.k.a. "75 SuperCab"

 

I had a similar problem, my headlights were blinking on and off after being on for a while. After replacing the headlight switch, the problem went away. I replaced the dimmer switch after that just because I had ordered one in case it was the problem. Both parts are cheap.

 

A common problem with the older style trucks is that the power for the lights fed through the switch making it switch overheat and fail prematurely. To correct this simply install a relay to control the power to the lights and allow the switch to control the relay. However, LMC has a wiring harness especially for this for around 30 bucks.

 

Just Replace the dimmer switch.

It is probably all corroded and has shorted out a circuit.

Fords don't have fuses for headlights. there is circuit breaker built in to them.

For the much preferred Relay headlight system.

https://www.ford-trucks.com/article/...r_Brights.html

 

I agree that it's probably the dimmer switch. You can just unplug the headlight plugs and test with your voltmeter to see if it is the low beam filiment. I would stay away from the LMC harness. One of the relays died after I had it installed for less than a month, and the replacement costs more from NAPA than the price of the harness. Check the article that Million mentions. I'd go that way.

 

You can get relays and connectors to make a great system here:
http://www.waytekwire.com/
They are also available at most electronic parts houses like:
http://eskc.com/default.asp
http://www.digikey.com/

Make a connector with those relay sockets that you can just plug one of the existing headlight connectors into so you can control the relay system. Some metal tabs soldered into a socket would do the trick then just plug on the connector to the tabs sticking up out of the socket.

 

Volvos have the Bosch relays in them.

 

All the power for your headlights goes through the dimmer switch check there first (remember it happened when he first turned on the lights). after you get headlights workingt do the relay mod it really works good.

 

Dimmer switch, Dimmer switch, Dimmer switch. Had a similar thing happen on 2 different rigs. Dimmer switch replacement is easy and inexpensive.

 

Very common problem...it's a bad dimmer switch. Ford # C0TZ-13A024-A

 

Seems to me that the general opinion is that I probably do have a bad dimmer switch. Even though I do expect that I will indeed be installing a replacement switch later today. Thanks to all of the wonderful technical information provided, as well as the advice on setting up a much better style of relay circuit for my headlights. I have now added another great upgrade to the project list for my truck! Considering the low cost and ease of installing this upgrade. I'm very sure that it's going to be moving up on my "To Do" list very quickly!

Once again "as always", the response I have received to this problem inquiry has exceeded my expectations! I would like to extend my sincere appreciation to everyone for all of the great information & assistance provided about this problem.

You guy's are the greatest!

Larry Bailey a.k.a. "75 SuperCab"

 

Hey all you guru's. I did a LED taillight upgrade top a 4inch by 1 inch card for the rear. When I hooked up the taillights I noticed the headlights were not coming on. The regular bulb socket had 3 wires. I hooked up these wires to the card and it works and looks great. What could possibly be wrong up front? I have replaced the light switch today (after reading this thread) no help still no headlights. I have check the wires to the front. The only power is in the running lights and sidemarkers. I am a little stumped. I am tempted to just override and go with the relay system that Mil1ion suggests.
Any help is appreciated.

 

Mr. 75 SUPERCAB, the other people here are most likely right about the dimmer switch. If by chance you still have the same problem after you install the new one, check to make sure the ground strap between the engine and firewall is in good shape. It is about a 6 inch long braided wire that is bolted on the upper left transmission bell bolt and goes right to the firewall.

Mr. 79 supercab400, go over all your connections again. Take them apart and resplice them. Also recheck your directions. The problem is likely to be something you inadvertantly caused much more-so than a new problem.