Right blinkers work but only tail light blinker works on left

[71gmcC15]

The blue and white wires do go throw the core support but i dont think it unplugs. Not a 100% sure but i will take a look tomarrow. Thares a hole the wirs pass throw in the core sapport and it has a black gromment looking thing that sits in the hole. Is the black grommet/ hole plug also a wire conecter. Like the one that conects the rear tail lights ?

[tutone]

I am sorry, your original post said tail light. I was assuming you were working on the rear of your truck. Same rules apply no matter where. You have to have power to the bulb, front or back of the truck.

[71gmcC15]

I gess i should of bean more clear the tail light workes fine its the frount im having issues with. So lets me be clear thare is nothing wrong with rear tail light. It works thw way is sappost to. The FRUNT park light does not blink when i go to use the left blinker. From what i understand the side marker is not suppost to blink. But the right one does. The right blinks work fine thoue. Its the left. I whant to get thr left side marker AND parlight to work. They do light up with my lights on. They just dont blink. So they do have power.

[Swar]

The front side markers ARE supposed to blink. The rear side markers do not. So ALL of your lights work including headlights? Just the front left amber markers (both) do not blink? Still sounds like a bad ground. You might wanna try attaching a ground wire or using a the test light to ground the big front marker socket. That is supposed to be grounded by the housing it sits in.

[71gmcC15]

ok yes you are correct just the amber dont blink on the left (both) i will try grounding the big socket on the front after school

[71gmcC15]

Originally Posted by tutone

Ok. your marker lights on the side of the truck should NOT blink. They are fed with dark brown wire as is the tail lamp and the license plate lamp. DO NOT GROUND it. tape it up if not in use. Your rear harness is hacked just like mine was. Google the tail lamp circuit for a 1969 or so chevy and get a diagram that shows you the color wires you need for each side. Now go to your harness plug on the drivers side frame rail and un plug th rear light harness from it. Take a meter or test light with your lights on. the one that is hot all the time is your brown wire. Send it to each side on the taillights and markers(side) and stub it off at your plate lamp if you don't have one. Next turn on your left blinker. Find the terminal in your harness that passes power on cycle. That is your left. The green wire is your back up lamps and the other one, forgive me I am color blind, is your right blinker. It should cycle power in the plug too. If you are not cycling power in the rear plug with your blinker on, then the problem is in your flasher or column. If all goes well plug it bag in and you will have it, If not report back.

but he said they dont now im confused i now on 69 they did not and 68 they did not light up but on 71 i think they do. i dont know

[Swar]

If yours is a 71, then yes, the front side markers are supposed to blink. I think 68 and 69 were just reflectors with no bulb. I think Tutone was referring to the rear side markers. But yea, bad bulbs or bad ground is the first thing to check for.

[71gmcC15]

Originally Posted by Swar

If yours is a 71, then yes, the front side markers are supposed to blink. I think 68 and 69 were just reflectors with no bulb. I think Tutone was referring to the rear side markers. But yea, bad bulbs or bad ground is the first thing to check for.

ok makes seance now

[VetteVet]

Here are your wiring diagrams for the markers and the trucks with marker turn signals . The first one is just the markers and the second is the markers that only flash in the front.





This is a PDF so I hope you can open it.

turn signal marker.pdf

[71gmcC15]

Originally Posted by VetteVet

Here are your wiring diagrams for the markers and the trucks with marker turn signals . The first one is just the markers and the second is the markers that only flash in the front.


Attachment 1748950


This is a PDF so I hope you can open it.

Attachment 1748953

thanks might help

[71gmcC15]

Ok i got a test light and found thaer is no power to the blinker. ( i just put the hazzards on ) Wich is blue wire right? I tryed to just wiggle the socket around the the housing and it did nothing it has a good ground on the housing. It light up fine on the white wire side.

[71gmcC15]

not sure what this is

[71gmcC15]

This is whare the white and blue wire go throw the core support

[71gmcC15]

This is the mess it runs into

[71gmcC15]

I just when out and tryed it again and i noticed when i turn mt headlights on the white wire light up like it is ment to but the blue wire has a little power . Not much it barrly lights the test light up. Is this normal?

[Steeveedee]

That's either a high resistance wire (maybe partially frayed or some strands cut in the wire) or a bad ground.

[71gmcC15]

I dont thinks its the ground i growndedit and it did not matter. I think i will unravel the tape and see if the wire is broke or frayed.

[VetteVet]

Originally Posted by 71gmcC15

Ok i got a test light and found thaer is no power to the blinker. ( i just put the hazzards on ) Wich is blue wire right? I tryed to just wiggle the socket around the the housing and it did nothing it has a good ground on the housing. It light up fine on the white wire side.

Your parking lights and turn signal lamps in the front are powered by a light blue(left) and a dark blue wires (right). These are the two turn signal light wires. The parking light wires are both Purple for both sides. I don't know where you are getting a white wire from. The light bulbs are grounded to the light housings, which are grounded to the core support. This is for Chevy trucks. I think the GMCs are the same.

The marker lights are not grounded to the fenders but they are grounded through the front turn signal lamps to the light blue and dark blue wires. Their power comes through the same brown wires that the signal lamps do.

If you look at the PDF I posted you can see that the brown wire for the marker lights go to each light and the wires coming out of the lights are wired into the power wires for the front signal lights, light blue for left and dark blue for the right light.

When the parking lights are on all four lights are lit by the brown wire and the front turn lights are grounded normally.

The marker lights are grounded through the front turn signal wires which have no power unless the turn signal switch is on for that direction.

When the turn signal switch is placed in the R or L turn, the marker light for that side will have power on the same wire LB or DB depending on which marker is working, L or R and will ground through the brown wire through the nearest light.

If the parking lights are on there will be power on the brown wires and when the turn signal switch is selected for L or R there will be power on the light blue or dark blue wires and the brown wires at the same time.

If you have 12 volts on both sides of the light at the same time the light will not light up.

It sounds confusing but it really is ingenious. If you notice when the turn signal is on, the front turn light and the marker light will flash alternately.


The light blue and dark blue wires come through the firewall block along with the purple wire for the parking light power for the L and R turn/parking lights.
You will have to check the light blue or the dark blue wires for bad connections or broken wires depending on which light is not working, If your parking lights are working then the lights have good grounds and the problem is on the power side.

Here is two diagrams that show the front turns with the purple wires and the light and dark blue wires going to the front lights. this one doesn't show the marker lights.





This one shows the front light wires and the markers but they don't flash.
If they flashed the ground wires from the markers would be connected to the front turn lights, dark blue and light blue wires instead of to the ground.

[VetteVet]

Your pic in post 37 is the fuse for the battery gauge on the alternator side. You will have one for the battery side near the terminal on the right fender.

The plug in post 38 is for the front parking/turn light and it is a connector not just a grommet.

[71gmcC15]

Originally Posted by VetteVet

Your parking lights and turn signal lamps in the front are powered by a light blue(left) and a dark blue wires (right). These are the two turn signal light wires. The parking light wires are both Purple for both sides. I don't know where you are getting a white wire from. The light bulbs are grounded to the light housings, which are grounded to the core support. This is for Chevy trucks. I think the GMCs are the same.

The marker lights are not grounded to the fenders but they are grounded through the front turn signal lamps to the light blue and dark blue wires. Their power comes through the same brown wires that the signal lamps do.

If you look at the PDF I posted you can see that the brown wire for the marker lights go to each light and the wires coming out of the lights are wired into the power wires for the front signal lights, light blue for left and dark blue for the right light.

When the parking lights are on all four lights are lit by the brown wire and the front turn lights are grounded normally.

The marker lights are grounded through the front turn signal wires which have no power unless the turn signal switch is on for that direction.

When the turn signal switch is placed in the R or L turn, the marker light for that side will have power on the same wire LB or DB depending on which marker is working, L or R and will ground through the brown wire through the nearest light.

If the parking lights are on there will be power on the brown wires and when the turn signal switch is selected for L or R there will be power on the light blue or dark blue wires and the brown wires at the same time.

If you have 12 volts on both sides of the light at the same time the light will not light up.

It sounds confusing but it really is ingenious. If you notice when the turn signal is on, the front turn light and the marker light will flash alternately.


The light blue and dark blue wires come through the firewall block along with the purple wire for the parking light power for the L and R turn/parking lights.
You will have to check the light blue or the dark blue wires for bad connections or broken wires depending on which light is not working, If your parking lights are working then the lights have good grounds and the problem is on the power side.

Here is two diagrams that show the front turns with the purple wires and the light and dark blue wires going to the front lights. this one doesn't show the marker lights.


Attachment 1749123


This one shows the front light wires and the markers but they don't flash.
If they flashed the ground wires from the markers would be connected to the front turn lights, dark blue and light blue wires instead of to the ground.

Attachment 1749124

Ok the white wire is the brown wire. It goes from brown to white on the connecter that goes throw the core support. The brown wire has power the light blue does not when i use the left turn signal. I know it has good ground. Im not vary smart when it comes to wiring. I dont see a purple wire. ( purple is what controlls the flash right?) on the diagram it shows it running to the light. I have light blue and brown. No purple.

[71gmcC15]

After almost a year I finally got it to work. It was just a lose wire under the dash in the moon shap plug haha