Hey all.. first post for your forum... it rocks.
so...
I have a 89 F-150 5.0L v8 efi 5sp manual 4wd.

The problem i am having is the headlights drop out intermittantly while driving. The lights work normally, but then after a period of time the lights will drop out for a short time (30s) then return. I loose the headlights, the parking lights, and the spotlights (newly installed by auto sparky just 2 days ago along with returning some dodgy wiring of the light switch back to original)

Longer story is the dude i bought the truck from had a on/off switch just for the headlights which i was removed to return to normal when the spotties were wired up. So i think the problem was there before, he has put his dodgy fix in and covered up any problems.

Searching your forums indicated that the headlights do not have a relay and therefore is loaded up when the lights are on causing heat damage to the female wiring harness plug.

So.. i have a spare light switch and i will check the wiring harness for any signs of melting or warping, and do a relay wiring mod for the headlights.

Am i heading in the right direction or has anyone experienced this before?

Any hints or tips for the headlight relay wiring mod? I have no idea and intend researching more now.

 

Yes, Ford has problems with their headlight switches and wiring plugs overheating. You can get a new plug with short wire pigtails for the switch and most any auto parts store(what does that tell you?). The headlight switch on the older trucks has a circuit breaker inside the switch, and if the switch gets too hot it will open this circuit breaker prematurely.

Your relay mod should get rid of all the problems, but I would inspect the switch and the plug carefully, and fix that if it doesn't look good. If you hunt around for all the parts, wires, etc., you may find you can't hardly do the relay mod for the cost LMC want's for their kit, and it plugs right in. Check it out and see if that's true.

 

Several years ago now, I installed Hella Vision + headlamp shells and 100+ watt H4 bulbs. Unlike Chevys, and a Jeep I once owned the small 18 gauge wiring in my '81 Econoline wouldn't support high current draw, leaving the headlights to cycle on/off. I installed one relay for each headlamp and upgraded all the wiring to 12 gauge right to the light sockets themselves and they've been stable ever since. Mind you these 130/100 watt H4's are aimed properly so's not to bling oncoming drivers.

 

I recently started having the same issue. I had just added some driving lights to my truck, wiring them to pull power from and switch on and off with the headlights. As soon as I added them, my headlights (and the driving lights, of course) started coming off and on intermittently. I rewired the driving lights to be on their own circut and switch, and that seemed to eliminate the issue...for a couple of weeks. Now, they've started doing it again, with the driving lights removed from the circut.

Do you think that I've killed my headlight switch? I was thinking that it was a relay overheating, but it seems there is not one in the headlight circut...should I just replace the headlight switch, or am I looking for something else that is wrong?

 

IF you're running a high amp circuit through a switch it may eventually fail, which is why I went with relays. The relay will protect the smaller wiring in the switch from high wattage (& amperage) H3 or H4 bulbs, and you can go from the relay to the lights with as heavy of gauge wiring as you'd like.