Headlight switch gone bad?

[dmw319]

Still can't get this problem figured out. Now the right blinker glows at times, so it doesn't seem to be consistent with left vs. right.

With the headlights off, all blinkers work as they should. With the headlights on, sometimes the blinkers work and sometimes they don't.

[dmjlambert]

Can you remove one of those tail light assemblies and show us what wires come from it? It takes 3 wires for a tail light to work,

1. brake light/turn signal power
2. tail lamp power that provides glowing light when headlights are on
3. ground

The ground connection is required for the brake light/turn signal light, and ground is also required for the tail lamp. In some assemblies the housing is metal and serves as ground if it is screwed to the truck without paint or rust interfering with the connection.
The brake light/turn signal is bright. The tail lamp is less bright.

[dmjlambert]

If you are able to remove the assembly you can test it. For a test battery you can use a lawnmower battery, or the truck battery with alligator clip test wires connected to it. Be careful not to short test wires because they will melt quickly.

Connect the negative lead of a test battery to ground lead or body of the assembly, then connect the brake light/turn signal power wire of the assembly to the positive lead of the test battery. The light should glow bright.
With the negative lead of a test battery still connected to ground of the assembly, connect both the brake light/turn signal power wire and the tail lamp power wire of the assembly to the positive lead of the test battery. The light should glow bright, perhaps slightly brighter than previous test.
Remove wires from positive terminal of battery.
With the negative lead of a test battery still connected to ground of the assembly, connect the tail lamp power wire of the assembly to the positive lead of the test battery. The light should glow, but less bright.

Moving over to the truck for testing, you can use a test light probe or multimeter to see which wires of the truck provide 12V when brakes are applied, and 12V when headlights are on.

Under the truck, the wires coming from the cab to the rear of the truck, colors of the wires should be:
brake light/turn signal power wire for left side = yellow
brake light/turn signal power wire for right side = dark green
tail lamp both sides = brown
ground = connected to frame or body of truck

[dmw319]

Originally Posted by dmjlambert

If you are able to remove the assembly you can test it. For a test battery you can use a lawnmower battery, or the truck battery with alligator clip test wires connected to it. Be careful not to short test wires because they will melt quickly.

Connect the negative lead of a test battery to ground lead or body of the assembly, then connect the brake light/turn signal power wire of the assembly to the positive lead of the test battery. The light should glow bright.
With the negative lead of a test battery still connected to ground of the assembly, connect both the brake light/turn signal power wire and the tail lamp power wire of the assembly to the positive lead of the test battery. The light should glow bright, perhaps slightly brighter than previous test.
Remove wires from positive terminal of battery.
With the negative lead of a test battery still connected to ground of the assembly, connect the tail lamp power wire of the assembly to the positive lead of the test battery. The light should glow, but less bright.

Moving over to the truck for testing, you can use a test light probe or multimeter to see which wires of the truck provide 12V when brakes are applied, and 12V when headlights are on.

Under the truck, the wires coming from the cab to the rear of the truck, colors of the wires should be:
brake light/turn signal power wire for left side = yellow
brake light/turn signal power wire for right side = dark green
tail lamp both sides = brown
ground = connected to frame or body of truck

Thanks for your reply, that is very helpful and ill have to give that a try.

Did you see my post #18? I posted a pic of the taillights wires

[dmjlambert]

I saw the post with the picture, but can't tell much about what is going on with that picture. It could be one of the 3 connections is cut off, perhaps the ground or other wire. I don't know if the assembly gets a ground connection through the housing, making the cut off wire unnecessary. Without all the info you'll have to experiment/test and see how it works.

[dmw319]

Thanks! I'll try to take better pics next time I'm able. with the rain/snow/cold weather/Christmas who knows when that will be

[Richard]

Believe dmjlambert is on the right track. I would guess cut wire is ground to tail lights. Reason brake lights work is bulb is grounding through the running light circuit. When lights are turned on the ground goes away because running light circuit is hot. Easy to check. At each tail light check for power to a body ground from two connected wires one at a time. Once with some one stepping on the brakes, then with the lights on. If you have power to both wires in each case just connect the third wire to ground. HTH.

[dmw319]

thanks, ill check it out. my tail lights and turn signals all work fine as long as the headlights are off. they are LED taillights, too.

[Richard]

Do the running lights work when lights are turned on and go off when brake is pressed?

[dmw319]

not sure about the running lights honestly. been too worried about turn signals. ill make a video of a walk around over Christmas break and post back up here.

[dmw319]

i forgot I made this video a while ago, it shows the issue with the left blinker staying half lit when I turn the headlights on.

https://www.youtube.com/watch?v=M4c3zyJ_Ijg

sometimes its the right side, sometimes it works fine. still cant nail down why its doing that. turn signals work fine when the headlights are off. but when they are on, the side that is half lit (usually the left) doesn't blink

[randy500]

Oh jeez....now u say u are running those stupid led taillights. All kinds of problems with led bulbs and turn signals beside your bad grounds.

[randy500]

If you want this problem fixed then remove the front and rear bulbs, alll 4 and then test the socket with a test light with the test light grounded where the bulb grounds (the side of the socket).
Fix the grounds either the socket/housing is bad or the housing is not grounded to the chassis.
Forget about all other symptoms until each socket is grounded and has power on one pin.
Taillight has 2 wires one stop turn, the other is running lights.
Front socket one wire is power in the other is power out to the side marker.

If you have a bad housing or socket replace with new housing or get a replacement socket from the parts store, pry the old socket out of the housing to insert the universal socket.

Very very very simple to fix this problem if you do the above....

[randy500]

I’m sure I already told u the dash turn indicator glows because the front turn signal bulb is bad or the housing is bad or not grounded. The indicator bulb on the dash is the last part of that circuit and glows when the bulb is bad.
The bulb is bad
The bulb is bad
The housing is probably bad
The housing is probably bad.
Did I mention there is a problem with the bulb and or housing and it’s in the front and on the same side as the glowing indicator bulb?

[randy500]

Try the LEd bulbs never, or at least after you have it all working with the type and size of bulbs the circuit was designed to use.

[randy500]

Dorman 85860 is an 1157 replacement socket with a ground tab which you can use to troubleshoot or repair your housings.

[dmw319]

thanks randy.

what is strange is that I've had the LED taillights since the PO installed them and this problem only started a couple years ago but I've owned the truck for years before that without issue and haven't changed anything regarding grounds (yes I know they can go bad after time).

100% there is no bad bulbs.

So using your theory, it's gotta be a ground. But it does it to both sides, but it is not always a problem. Sometimes one works, sometimes both work. its very strange.

What is the best way to ground the LED taillight housing?

[randy500]

Best way to ground the led housing is to remove them, place them on the ground, they will be grounded for the purposes of fixing your problems.

Fix the circuits with incandescent bulbs then introduce the led problem to the system.

You do realize the lights flash due to high electrical load? LEDs unmodified do not create enough of a load for the lights to flash?

[dmw319]

Originally Posted by randy500

Best way to ground the led housing is to remove them, place them on the ground, they will be grounded for the purposes of fixing your problems.

Fix the circuits with incandescent bulbs then introduce the led problem to the system.

You do realize the lights flash due to high electrical load? LEDs unmodified do not create enough of a load for the lights to flash?

with headlights off, they function 100%. it is only with the headlights turned on, that one side (sometimes) won't blink.

[randy500]

Sounds like a bad bulb, when power is introduced from the running light to the circuit the power interrupts he ground path, one filament is shorted to the other inside the bulb or the led circuitry.
Change out old bulbs and leds for new.

The side that glows is either bad bulb or bad housing.

I assume the tail lights are some sort of led panel and you cant just install a normal bulb?

[dmw319]

Originally Posted by randy500

Sounds like a bad bulb, when power is introduced from the running light to the circuit the power interrupts he ground path, one filament is shorted to the other inside the bulb or the led circuitry.
Change out old bulbs and leds for new.

The side that glows is either bad bulb or bad housing.

I assume the tail lights are some sort of led panel and you cant just install a normal bulb?

You keep saying its a bad bulb, but I have literally replaced every single bulb one at a time and they all still function properly without headlights on. And both sides have glown (is that a word? ) at some point. So there is no consistency to the issue.

And correct, its an led panel where I can't install a normal bulb. I do believe I have the original taillights and harnesses in a box, so maybe I could try those out.

[randy500]

The standard procedure for fixing anything is to replace suspect or non factory components with factory.

Start there and then introduce the faulty parts, which are probably the leds, they have circuitry inside of them which could be causing problems when the headlights are turned on, such as power bleeding from the running lights to the turn signal circuit.

Go back to factory new bulbs and see what happens. Just because the led lamps worked right 2 years ago doesn’t mean they are good now.

[dmw319]

Originally Posted by randy500

The standard procedure for fixing anything is to replace suspect or non factory components with factory.

Start there and then introduce the faulty parts, which are probably the leds, they have circuitry inside of them which could be causing problems when the headlights are turned on, such as power bleeding from the running lights to the turn signal circuit.

Go back to factory new bulbs and see what happens. Just because the led lamps worked right 2 years ago doesn’t mean they are good now.

ill see if I can dig up the old taillights and go from there

[randy500]

Or buy the bulb holder that I posted, add connectors to plug it into the tail light or front lights to see if you have a housing ground problem.

[dmw319]

bulb holder you posted? sorry I must have missed that.

I do have a test light and voltmeter I can use.