Right blinkers work but only tail light blinker works on left

[71gmcC15]

Im new to the forums so dont bite my head off. I have a 71 gmc c15. I have looked for this in the seach fountion and could not find any thing. The right blinkers work fine but the left only the tail light blinks . Slowly i may add. It also dont have the green arrow on the dash when i go to use the left blinker. Same with hazzards. High beams does not affect it. I dont think its a ground but maby. It some times works. Like 5% of the time. It also has a new relay and hazzard swich. No bulbs are burnt out. So im cunfused

[Duck 37]

I'd check the ground and check for corrosion at the contact points,including the sides of socket and the bulb.

[71gmcC15]

Whare does it normal ground at ? I herd buy the frount bumper. Have to look tomorrow.

[71gmcC15]

Ignor figering out how to post pics

[LockDoc]

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Read through this thread on the grounds....

http://67-72chevytrucks.com/vboard/s...t=ground+strap

LockDoc

[71gmcC15]

Thanks but i dont think ground straps are the issue. The ground on the lights them selves is what im looking for. I will look for it when its nice out again.

[tutone]

I will take a stab at this. First off, did they work and just quit working? My bet is that you have an incomplete circuit on your left side. Two suspect places to look first. Your tail light housing .make sure your brown wire and your yellow wire have a good connection . If need be, add a ground from the housing mounting screw to the frame. Now your turn signals go through your cancellation switch under your steering wheel as well. Pull your wheel and inspect the operation of the switch. If you have a cheap test light, you can se if you are passing power at the switch. Lastly swap your hazard flasher with your blinker flasher. Do all these things one at a time and check for results as you go. Same with my truck. The rear harness was hacked beyond belief.

[71gmcC15]

They light up just dont blink. Just random when they do blink .I will check the wires and relays when its not -10 F. Thanks for the help

[Andy4639]

Originally Posted by 71gmcC15

They light up just dont blink. Just random when they do blink .I will check the wires and relays when its not -10 F. Thanks for the help

Locate the half moon turn signal plug under the steering column. Check the wiring diagram and place a test light in each wire output for the signals and turn the signals on and see if the test light blinks, if not its in the blinkers are the grounds If it does it's at the bulb locations are some where after the plug in.

[Swar]

I've had this problem before. Probably bad ground on front marker light housing. Reach under there and spin the bulb socket back and forth in the housing, that's your ground.

[71gmcC15]

I found a wire about in the middle of thr pickup under the tailgate. Is ether black or dark brown cant tell i tryed grounding it and it did nothing. ( i got to get a test light). Is it for the licen plate lights i dont have or what. I will check the wireing diagram. Just cheked it its for the licen plate lights

[71gmcC15]

Originally Posted by Swar

I've had this problem before. Probably bad ground on front marker light housing. Reach under there and spin the bulb socket back and forth in the housing, that's your ground.

I tryed it and it did nothing if it was a bad ground it would light up at all right? It lights up when i turn my lights on. All my lights work and the tail light blinks on the left just not the side marker or park light. And all of them blink on the right.

[Swar]

Dang, thought that would do it. You sure it's not the bulb? Sometimes the filament will break apart but look like it's still intact. Try different bulbs if you haven't already.

[71gmcC15]

Originally Posted by Swar

Dang, thought that would do it. You sure it's not the bulb? Sometimes the filament will break apart but look like it's still intact. Try different bulbs if you haven't already.

It light up so is not the bulb. Is it a duel elmeny 194? I dont understand how that could be cuz the other side works. my low beam headlight out but on the right side. That cant be the reason. Can it? If i use high beam it chages nothing. Remeber i have 4 headlights.

[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.

[71gmcC15]

Ok so the frount side markers dont blink. My right one does and i thought just the frounts blinks. If the dont then basicly what you are saying is to start over with the harness. Ok i could do that. but some times the left blinkers do work with the side marker blinking. I would love to just get it working that way. My left park light doent blink ether is that the same problum.

[71gmcC15]

I also am a bit of a wiring noob so as i can see the yellow wire is the left turn single. I what to know whare it goes from the plug on the fram up tord the cab if i can find that wire then i can spice into it and run it to the park light and side light. But my other ? Is if i do that do i just splice into the brown wire on the side marker and wich wire in the parligh? blue or white?

[zosoppp]

Originally Posted by 71gmcC15

I found a wire about in the middle of thr pickup under the tailgate. Is ether black or dark brown cant tell i tryed grounding it and it did nothing. ( i got to get a test light). Is it for the licen plate lights i dont have or what. I will check the wireing diagram. Just cheked it its for the licen plate lights

Yes that is for the licence plate light. It should be brown but likely is dirty. Do not ground it. Brown is the "parking light" power wire.

[zosoppp]

Originally Posted by 71gmcC15

I also am a bit of a wiring noob so as i can see the yellow wire is the left turn single. I what to know whare it goes from the plug on the fram up tord the cab if i can find that wire then i can spice into it and run it to the park light and side light. But my other ? Is if i do that do i just splice into the brown wire on the side marker and wich wire in the parligh? blue or white?

It goes into the rear frame harness (4 wires, brown, yellow, green, dk green) connector and runs along the left frame rail up the front of the firewall behind the left head (on a v-8) and connects to a 4 connector socket at the firewall.

The parking and side marker lights should be on the brown wire and ground to the body.

[71gmcC15]

Originally Posted by zosoppp

It goes into the rear frame harness (4 wires, brown, yellow, green, dk green) connector and runs along the left frame rail up the front of the firewall behind the left head (on a v-8) and connects to a 4 connector socket at the firewall.

The parking and side marker lights should be on the brown wire and ground to the body.

Ok the side markers are on a brown and black but the parks are white and blue and it looks factory. i will have to look at it closer . Thaer is a big bundle of wires raped in tap on the left side of the firewall. Ill un rap that tommarow and see if any thing looks funny.

[zosoppp]

Originally Posted by 71gmcC15

Ok the side markers are on a brown and black but the parks are white and blue and it looks factory. i will have to look at it closer . Thaer is a big bundle of wires raped in tap on the left side of the firewall. Ill un rap that tommarow and see if any thing looks funny.

my comments about the 4 wire bundle are for the rear cause we were also discussing the rear license plate light.

The front wires are not nearly that simple and do not run along the left frame rail to the firewall.

instead they come out of the bulkhead connector, through the left fender and out again up by the left headlight/regulator/horn.

[71gmcC15]

Originally Posted by zosoppp

my comments about the 4 wire bundle are for the rear cause we were also discussing the rear license plate light.

The front wires are not nearly that simple and do not run along the left frame rail to the firewall.

instead they come out of the bulkhead connector, through the left fender and out again up by the left headlight/regulator/horn.

Ok i taped up my licen plate lights so no need to worrie about that and i know whare you are talking about the wires along the fender thet go into the bundle of taped wires on the left on the core sapport. So i will untape the mess and see what im dealing with. Hopefully its just a broken wire or bad ground. I am not good at wireing. Thank you for the help. God knows i need it.

[zosoppp]

Originally Posted by 71gmcC15

Ok i taped up my licen plate lights so no need to worrie about that and i know whare you are talking about the wires along the fender thet go into the bundle of taped wires on the left on the core sapport. So i will untape the mess and see what im dealing with. Hopefully its just a broken wire or bad ground. I am not good at wireing. Thank you for the help. God knows i need it.

Before you pull apart the wiring, use a test light or a multi meter at the connector for the front signal.
https://www.harborfreight.com/6-12-v...ster-4288.html


Take the bulb out and clamp the test light wire or negative test probe to a good ground. There is a ground connection screw near the external regulator behind the left headlight.

Check that you have voltage/light at each of the two bulb contacts when the parking or turn signal are on.

[71gmcC15]

Originally Posted by zosoppp

Before you pull apart the wiring, use a test light or a multi meter at the connector for the front signal.
https://www.harborfreight.com/6-12-v...ster-4288.html


Take the bulb out and clamp the test light wire or negative test probe to a good ground. There is a ground connection screw near the external regulator behind the left headlight.

Check that you have voltage/light at each of the two bulb contacts when the parking or turn signal are on.

Will do. But if i do not understand what that will do. If i dont have power the bulb wouldnt light up right? Or does it not need power at both contacts. Oo its a duel elament in the frount so one will have power with the lights on then the ohter contact will have power when i use the blinker. Or am i way off?

[zosoppp]

There might also be a connection point right behind the signal where the wires pass through the radiator core support. It might be good to "exercise" this carefully, meaning disconnect it, maybe clean or apply dielectric grease and reconnect.

I am not certain how different a 71 gmc would be from a 70 chevy in this regard maybe someone else can