71 GMC lights and blinker problem need help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mttnlsn · 02-18-2010, 06:18 PM

I am working on a 71 gmc 3/4 ton 2x4. My problem is when the head lights are OFF my blinkers work correctly. When my blinkers are off my head lights work correctly. When my headlights are on and I try my blinkers my dash board lights blink, the blinker arrows are lit up. When I switch from hi to low beam half my dash board lights go out all together? If I turn my light dimmers down all the way the blinkers work better, but not perfect. I have installed a new light switch and blinker wiring harness in the column. Any ideas?? This is killing me. I hate electrical problems. Thanks for the help. This is my first post.

PanelDeland · 02-18-2010, 06:57 PM

Welcome!!! I'll tell you the same 2 things everyone else will.Check your grounds.Most electrial problems with these trucks are due to bad grounds and it sounds like that is what you have.Also check your connections at all connectors and for bad splices.40 year old trucks tend to have been messed with a bit and adding trailer lights,fog or driving lights and such was common.Anywhere these have been spliced in may cause a problem.

mttnlsn · 02-23-2010, 06:51 PM

thx for the help i will check it all again. the lite swich grounds to the dash, do you know where does the blinker swich ground? or the color of the ground wire for the blinker swich?

**Stocker** · 02-23-2010, 06:58 PM

Welcome to the boards from N. Calif!

Sounds like a can-o-worms, and possibly more than one problem.

When the turn signals don't work, but the green arrow lights up in the dash, the problem might be bad grounding of the front side marker lamps. Happens more often in damp weather. They ground through their mounting screws.

mttnlsn · 02-23-2010, 07:20 PM

thanks for the help on that. i will go out and have a look at the lights on that. my son installed them so i will double check. i hate electrical problems.

**Classic Heartbeat** · 02-23-2010, 07:44 PM

Sounds like to me something is wired wrong. Who wired the turnsignal switch? Nobody that I know of sell just the turnsignal switch wire harness. Could also have a bad dimmer switch. (doubtfull but could) Grounding is always an issue if not done correctly, but the problems that you discribe are more than that. Sounds like you are getting power feeding back through the harness somehow. This is why I asked about the turn signal switch harness. WES

mttnlsn · 02-24-2010, 11:12 AM

bought new turnsignal switch harness from Classic Parts of America product code 53-510 and installed it. When i unhitch the harness from the pickup the head lights and dash lights and dimmer work properly. when i rehook up the turnsignal harness to the truck and leave the lights off the blinkers work properly. when i turn on the lights and try the blinkers they work but not with the same spark as when the lights are off. when the lights are on and i use the turnsignal lights on the dash are on. they will kinda blink if i turn on them on. bad deal is the problems are not always the same. Yes i agree i am getting back feeding to the dash or to the new turn switch. i have checked all the grounds i can find. cleaned them and replaced with no help. i am going to order a wireing diagram for the truck from Classic parts $4.95 and study it for a while. thanks for the hlep any ideas are always helpfull.

monte0185 · 02-24-2010, 01:01 PM

Check your turn signal sockets. Occasionally one will not have a good ground or will be shorted out. You can unplug the rear at the frame and try it again that way it narrows it down to front or back. Did you check the little clip on ground behind the instrument cluster? Its just a clip on one for the cluster everyone forgets about. Just a few random thoughts.

**Classic Heartbeat** · 02-24-2010, 01:18 PM

53-510, shows to be a turn signal switch. It is the lator model switch with adapter. I personaly don't like that switch, because there is a direct replacement switch that has the red hassard button like the originals have and the half moon plug. They do not use the adapter like the one from Classic Parts, witch is probably your problem. We sell them for $39.95 like they do (53-510A)and can't seem to keep them in stock..lol I have used them many times and am extreemly happy with them. WES

northerngmc · 02-24-2010, 01:28 PM

I had the same problem last fall. When I turned the headlights on the turn signals would not work.

I found out that the ground wire from the bottom of the cab to the frame was broken. Fixed that and the problem disappeared.

Check your ground wires or simply install a wire from the cab to the frame.

cdowns · 02-24-2010, 03:06 PM

in order to work properly each and every light bulb needs to b grounded

02-18-2010, 06:18 PM	#1
mttnlsn Registered User Join Date: Feb 2010 Location: Iowa Falls, Iowa Posts: 6	71 GMC lights and blinker problem need help I am working on a 71 gmc 3/4 ton 2x4. My problem is when the head lights are OFF my blinkers work correctly. When my blinkers are off my head lights work correctly. When my headlights are on and I try my blinkers my dash board lights blink, the blinker arrows are lit up. When I switch from hi to low beam half my dash board lights go out all together? If I turn my light dimmers down all the way the blinkers work better, but not perfect. I have installed a new light switch and blinker wiring harness in the column. Any ideas?? This is killing me. I hate electrical problems. Thanks for the help. This is my first post.

02-18-2010, 06:57 PM	#2
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: 71 GMC lights and blinker problem need help Welcome!!! I'll tell you the same 2 things everyone else will.Check your grounds.Most electrial problems with these trucks are due to bad grounds and it sounds like that is what you have.Also check your connections at all connectors and for bad splices.40 year old trucks tend to have been messed with a bit and adding trailer lights,fog or driving lights and such was common.Anywhere these have been spliced in may cause a problem. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

02-23-2010, 06:51 PM	#3
mttnlsn Registered User Join Date: Feb 2010 Location: Iowa Falls, Iowa Posts: 6	Re: 71 GMC lights and blinker problem need help thx for the help i will check it all again. the lite swich grounds to the dash, do you know where does the blinker swich ground? or the color of the ground wire for the blinker swich?

02-23-2010, 06:58 PM	#4
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,698	Re: 71 GMC lights and blinker problem need help Welcome to the boards from N. Calif! Sounds like a can-o-worms, and possibly more than one problem. When the turn signals don't work, but the green arrow lights up in the dash, the problem might be bad grounding of the front side marker lamps. Happens more often in damp weather. They ground through their mounting screws. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay Last edited by Stocker; 02-23-2010 at 06:59 PM.

02-23-2010, 07:20 PM	#5
mttnlsn Registered User Join Date: Feb 2010 Location: Iowa Falls, Iowa Posts: 6	Re: 71 GMC lights and blinker problem need help thanks for the help on that. i will go out and have a look at the lights on that. my son installed them so i will double check. i hate electrical problems.

02-23-2010, 07:44 PM	#6
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,766	Re: 71 GMC lights and blinker problem need help Sounds like to me something is wired wrong. Who wired the turnsignal switch? Nobody that I know of sell just the turnsignal switch wire harness. Could also have a bad dimmer switch. (doubtfull but could) Grounding is always an issue if not done correctly, but the problems that you discribe are more than that. Sounds like you are getting power feeding back through the harness somehow. This is why I asked about the turn signal switch harness. WES __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys

02-24-2010, 11:12 AM	#7
mttnlsn Registered User Join Date: Feb 2010 Location: Iowa Falls, Iowa Posts: 6	Re: 71 GMC lights and blinker problem need help bought new turnsignal switch harness from Classic Parts of America product code 53-510 and installed it. When i unhitch the harness from the pickup the head lights and dash lights and dimmer work properly. when i rehook up the turnsignal harness to the truck and leave the lights off the blinkers work properly. when i turn on the lights and try the blinkers they work but not with the same spark as when the lights are off. when the lights are on and i use the turnsignal lights on the dash are on. they will kinda blink if i turn on them on. bad deal is the problems are not always the same. Yes i agree i am getting back feeding to the dash or to the new turn switch. i have checked all the grounds i can find. cleaned them and replaced with no help. i am going to order a wireing diagram for the truck from Classic parts $4.95 and study it for a while. thanks for the hlep any ideas are always helpfull.

02-24-2010, 01:01 PM	#8
monte0185 Registered User Join Date: Oct 2008 Location: Brighton, TN Posts: 1,267	Re: 71 GMC lights and blinker problem need help Check your turn signal sockets. Occasionally one will not have a good ground or will be shorted out. You can unplug the rear at the frame and try it again that way it narrows it down to front or back. Did you check the little clip on ground behind the instrument cluster? Its just a clip on one for the cluster everyone forgets about. Just a few random thoughts. __________________ A computer once beat me at chess, but it was no match for me at kick boxing. Duct tape is like the force. It has a light side, a dark side, and it holds the world together.

02-24-2010, 01:18 PM	#9
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,766	Re: 71 GMC lights and blinker problem need help 53-510, shows to be a turn signal switch. It is the lator model switch with adapter. I personaly don't like that switch, because there is a direct replacement switch that has the red hassard button like the originals have and the half moon plug. They do not use the adapter like the one from Classic Parts, witch is probably your problem. We sell them for $39.95 like they do (53-510A)and can't seem to keep them in stock..lol I have used them many times and am extreemly happy with them. WES __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys Last edited by Classic Heartbeat; 02-24-2010 at 01:21 PM.

02-24-2010, 01:28 PM	#10
northerngmc Registered User Join Date: Jan 2004 Location: Whitehorse YK Canada Posts: 2,651	Re: 71 GMC lights and blinker problem need help I had the same problem last fall. When I turned the headlights on the turn signals would not work. I found out that the ground wire from the bottom of the cab to the frame was broken. Fixed that and the problem disappeared. Check your ground wires or simply install a wire from the cab to the frame. __________________ Blaine 59 GMC 9314 a.k.a. Whoopee 68 C20 50th Anniversary a.k.a. The Rat http://www.flickr.com/photos/northerngmc/ http://www.members.tripod.com/P-wee/index_032.htm 1.61803 is one H of a lot better than 3.14159, no really it is!

02-24-2010, 03:06 PM	#11
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 71 GMC lights and blinker problem need help in order to work properly each and every light bulb needs to b grounded __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY



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