Headlights won't dim

[tampabronco]

Replaced the floor mounted dimmer switch and then replaced the connecting wire harness. Have headlights but can't get to change.

 

[Broncobowsher]

Any LEDs? Relay upgrade harness?
What happens if you leave the high beam switch unplugged?

 

[tampabronco]

Any LEDs? Relay upgrade harness?
What happens if you leave the high beam switch unplugged?

Been running LEDs for years with no issues. Thinking it might be a bad headlight switch?

I also recently did a alternator upgrade and removed voltage Regulator... Wonder if that has anything to do with it

 

[DirtDonk]

With stock wiring neither of those things has any effect.
The headlight switch only sends one voltage signal over one wire that goes down to the dimmer switch on the floor.
That floor switch is where they split between low and high beam.

Alternator also has literally zero affect on the headlight circuits.

The only way either of those two can give you this issue is if during the installation someone buggered up the wires.

 

[DirtDonk]

Relay upgrade harness?

Hey tampa, what about this question?

What happens if you leave the high beam switch unplugged?

And what about this one too?
Easy to do, just unplug it again to see what happens. If the lights go out, then do another test by re-connecting it and with a test lamp or volt-meter probe the back of the switch to see if power switches from one wire to the other.

But first things first. No matter what the general condition of things is, check your grounds. Make sure the body has a dedicated ground wire from the negative terminal to the body.
From the factory this ground was on the wheel well near the starter relay/solenoid. Once the original ground cable is changed you have to renew the body ground. Mounting it to one of the bolts existing for the old ground or for the starter relay works well.
Then check the wires that ground the headlight harnesses to the core support. Remove the nuts, clean all the wires/terminals and body underneath, then re-attach them with the nuts. If there's enough rust or paint built up it can mess with things. The filaments might be self-cancelling each other and the one with the least resistance (the low beam I think) will get the power and the other becomes the ground. Maybe...
I really don't know how it all works all the time, and even when I sleep at a Holiday Inn Express I can't always figure it out!
But whenever you have a wonky electrical problem, you probably have a wonky ground somewhere.

If you have headlight relays then you need to do some further testing along those lines.

Paul

 

[tampabronco]

Hey tampa, what about this question?


And what about this one too?
Easy to do, just unplug it again to see what happens. If the lights go out, then do another test by re-connecting it and with a test lamp or volt-meter probe the back of the switch to see if power switches from one wire to the other.

But first things first. No matter what the general condition of things is, check your grounds. Make sure the body has a dedicated ground wire from the negative terminal to the body.
From the factory this ground was on the wheel well near the starter relay/solenoid. Once the original ground cable is changed you have to renew the body ground. Mounting it to one of the bolts existing for the old ground or for the starter relay works well.
Then check the wires that ground the headlight harnesses to the core support. Remove the nuts, clean all the wires/terminals and body underneath, then re-attach them with the nuts. If there's enough rust or paint built up it can mess with things. The filaments might be self-cancelling each other and the one with the least resistance (the low beam I think) will get the power and the other becomes the ground. Maybe...
I really don't know how it all works all the time, and even when I sleep at a Holiday Inn Express I can't always figure it out!
But whenever you have a wonky electrical problem, you probably have a wonky ground somewhere.

If you have headlight relays then you need to do some further testing along those lines.

Paul

The headlights go out when I unplug the dimmer switch. I will put a meter on it this evening. Guessing I need to check my grounds

Should I order relay headlight switch from WH?

 

[Broncobowsher]

The high beam switch is just a splitter. 3 wires. One has power from the headlight switch when you turn the lights one. The other 2 wires, one is low beams, the other high beams. One or the other. You can put in a jumper to bypass the switch.

There can be weird things in the headlight as well since it is LED. If there is an internal short in one, it could be activating both high and low beams. That could also cause the other headlight to light both as well being back fed on the off circuit.

Are you sure the high beams are really stuck on? Not just the lights aimed poorly? Or LED lights that have a poor cutoff pattern that look like high beams all the time? What LED lights are you running? You stated you have been running them for years. Years ago the LED lights had horrible beam patterns that were like high beams all the time, even on low. Only in the past couple of years have good LEDs hit the market in mass.

 

[DirtDonk]

You can also test the wires up at the lights when you jumper the floor switch connector.
Put a jumper wire between the center wire(?) and either one of the side wires. Now you know for a fact that you have 12v going to only one circuit. Whether it's high or low does not matter at this point.
Then go up to the headlights and disconnect their 3-wire plugs from the body harness and measure voltage at the connector.
Obviously, only one wire should have power. Using the volt-meter you can test for voltage at either wire AND the ground in the same connector.

If you have consistent power to only one wire terminal in the connector, then that circuit would appear to be good.
Go back into the cab and swap the jumper wire to the other circuit and re-check at the lights to make sure the power moved to the opposite wire..
If it did, then your wires are fine. Re-connect one headlight and once it's illuminated go back and swap the jumper once again. When you do this the beam pattern should change. If it does not, you have a problem with the light.
If it does change between low and high, re-connect the floor switch and re-check for function. If it still does not change with the floor switch, then your new floor switch is defective.
As usual...

Paul

 

[DirtDonk]

As usual I made that needlessly complex by breaking it up too soon.
Once you install the jumper and turn the headlight switch on, you can swap the jumper to the other wire and watch the headlight function. If they switch beams like they should, then you know right off that the floor dimmer switch is the culprit.

Obviously, this testing is likely to be easier after dark. But if you have a good wall in the garage you can probably get it all done in the daylight. Especially with bright LED's.

Paul

 

[DirtDonk]

Should I order relay headlight switch from WH?

Of course!!!
In reality though, if your lights worked fine without them, then you don't really need them now.
LED's use less current so the master headlight switch is not under as big a load as it would be with normal lights. However, some LED's respond to a more stable and higher voltage input that can be had with relays.
Again, if yours work fine, you don't need them. If there are any questions in the future about an issue, then a relay kit might be the way to go.

Relays were one of the earliest mods I did to my '71 after disc brakes. Both for the headlights and for the horns. Big difference in both and glad I did it.
That was with high output H4 halogens of course, so power consumption was a factor. Losing my headlights on a pitch black rural highway one dark night was the real instigator though!

Paul

 

[gnpenning]

It's been awhile, but the high beam wire at the foot switch should have a double wire on the plug side. One is for the high beam indicator light the other goes to the headlights. This should help you narrow down which is the high beam wire.

 

[gr8scott]

I always carry jumpers...anything can happen. Talk about a pitch black rural highway..
.

 

[DirtDonk]

Yeah, seen that switch a time or two.
Just like the old ignition switch that falls out from the back of the dashboard and leaves you without power for awhile.