Good afternoon ladies and gents! I have had this problem with my headlights where they flicker on and off when they want to for a while but its been worse lately. Usually if I just use my low beams then there is no problem but if I try to use my high beams the lights will flicker on and off. Turning them off and right back on again doesn't help but if I leave them off for like a minute or so then turn them back on they work fine for a while. The head light bulbs are new, so is the switch in the cab

 

Check relay in fuse box under hood. Your talking about the headlight switch is good, or the high low beam switch? In the cab.

 

I changed both of them in February so they should be fine. Where is the relay?

 

Should be in a plastic box under the hood that is labeled fuses. I believe the relay lives in there. Should be imprinted under the plastic cover once you remove....if it is the same as mine.

 

Ok I'll take a look

 

How do I know if it's bad?

 

If you are sure both high low switch and headlight switch are good, which you said they are. How did you check them? . Also check the wiring is not frayed and also check both headlight connectors to make sure they are in very good shape with no damage or loose wires. I will need to look again at the schematic. The headlight relay I believe just turns them on...it wouldn't necessarily only the high beams on, so that may not be the issue, but still worth checking to make sure it is plugged in good.

Also, if you have "upgraded" with higher wattage bulbs it could be overheating the circuit causing the issue. If you can disconnect one of the low beams and then turn on the high beams and no flicker, then you need to look at the wattage of the bulb and look at the sockets for signs of overheating.

You can test the relay with a multimeter, but you have to know how to use it. Pull the relay out of its socket and check across the coil with the ohmmeter section of the multimeter. It should read low resistance, under 100 ohms. If it reads higher, the coil of the relay is bad.

 

Check the grounding for your lights, I've seen similar issues where a ground for the headlights had some rust build up between the wire and frame connection points. Trace the ground wires to where they bolt onto the frame then use a wire brush to clean that spot up really well.

Usually the rust will conduct until heated and then will start to cut out, hence the flickering and intermittent connections.

Just a thought, and a free fix if it is the problem.

 

Thanks ill take that into consideration. I haven't been able to find the relay. I only found the fuel pump and EEC relays. They're isn't even a spot for one

 

There is no relay for the headlights from the factory.

The headlight switch and maybe the connector are probably the issue.

I upgraded to a headlight relay harness to keep the load off of the factory switch and to provide more voltage to the headlights.

 

So what do you recommend looking at?

 

I don't think you have relays.

I just went through this on my 88 f150.

In my case it was the low beams that were flickering.

As others have said - new high wattage bulbs can draw more current and stress out wires. LMC sells a relay kit for around $30 - I might be tempted to buy that and see if the problem goes away.

But - if like me you're using normal bulbs - I'd guess you have a short or a loose connection somewhere.

You've got two facts that help narrow things down.

1.) It only happens on high beams - so the problem has to be at or after the hi/low switch. You've replaced the switch - so it has to be after.

2.) Because it only happens on high - it's PROBABLY not a ground problem as both high and low share the same ground wires.

From the hi low switch - there are two wires - on for the high beam filaments, one for the low.

The wires on mine (88 f150) run in a harness along the drivers side fender.

Each wire breaks into two wires in the harnerss - one for the left light, one for the right.

This split (on mine) happens towards the front of the engine compartment. And that's where MY problem was. I had to redo those splices. I had to remove my washer/overflow box to get to it (along with unwinding miles of electrical tape from the harness)

The ground wire also runs through there.

If you want to rule the ground wire out completely - tap into it with a temporary wire and go directly to the negative terminal on your battery - and re test the lights.

On mine - I cut the wire coming near the firewall (in my case the low beam wire). Locating it wasn't TOOOOO bad, just took a while...

Then I ran a test wire from the cut end to a test light. No short. so I knew my problem was after the fire wall connection.

That's kinda what you need to do - cut/bypass/isolate.

I took a guess that the wires themselves were fine and the logical place to look for a problem was in that division point - and I got lucky - that's where it was.

Just be damn sure that if you cut any wires that you splice them back together properly and wrap them well. Otherwise a year down the road you're going to be back in the same boat.

 

there are only two things that would cause this.
a bad electrical connection on the headlight switch, or bad connections on the dimmer switch.

pull the headlight switch, remove the wires from he back of the switch and closely inspect the switch and plug for burn marks. if anything looks funny, replace it with a new wiring pigtail. they are readily available from any good parts store.

if everything is good with the headlight switch, fold back the floormat/carpet and remove the dimmer switch from the floor. 2 bolts. remove the wires and closely inspect the switch and wires. if anything looks funny replace the switch and wiring pigtail. as with the headlight stuff, the parts are readily available from any good parts store

 

I do remember some slight burnt spots on the headlight switch connector. I'll have to go check them out tomorrow.

 

The wiring diagram for most Ford trucks shows a circuit breaker built into the main light switch. Had this go bad on a Dodge that had it do the same trick. Fooled me for a while as the switch contacts all looked OK for the vehicle's age. The breaker resets itself, sometimes fairly quickly if it cools off fast enough.

Joe