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1990 gmc Sierra. The factory brake signal box My brake lights went out but all other lights work on rear end. There is a white wire hanging out from under dash that runs to brake control box. Where does it connect and what is the wire for???

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  • Cars & Trucks Master
  • 3,679 Answers

Depress the brake pedal whilst connecting a volt meter to this white wire , if you get power it's to do with the brake switch , if no power then just a spare wire dropped down and no need to worry any further about this wire , so if it did show power remove the brake switch/control box and see if it's obvious where the wire fits , get a workshop manual to help as these manual are invaluable with step by step guides ,etc

Posted on Jun 14, 2014

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Posted on Jan 02, 2017

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SOURCE: 1997 gmc 3500 box truck. no brake lights. changed

Check the fuse.

Posted on Sep 18, 2009

pops296
  • 174 Answers

SOURCE: my trailer wiring on my 2001 gmc sierra

First replace the trailer light brake/turn signal fuses. I have seen where the fuse will show good, but loose connection in the block. You can easily do it by using the flashers. Using a test light you can check power in and out of the fuse. Just touch the tester to the metal pin on top of the fuse... on both sides. Power in and power out. If power is there on both sides and still nothing below the fuse box, the box is bad. Not a common problem. Also check http://www.etrailer.com/faq-wiring.aspx.

Posted on Jan 29, 2010

  • 432 Answers

SOURCE: 1990 GMC Sierra 1500 pickup. Windshield wipers, Cruise Control

May want to look at replacing the wiper circuit board.It is located on the firewall adjacent to the wiper motor and has a some what square black cover with 3 torx screws and wireing harness pluged into the side.We had a truck that every time you washed it the wipers would stay on until it dryed out.You can try removing it and spaying it down with contact cleaner just watch the brease on the two contact tips.Well hope this helps.

Posted on Feb 05, 2010

ftw1952
  • 10319 Answers

SOURCE: wiring diagram for 1996 gmc sierra brake asembly

The brake light switch is at fault. Get a new one and replace it. The location is at the brake pedal area mounted on a bracket with a plunger stud that rest on the brake pedal's arm the pad is attached to

Posted on May 08, 2010

  • 553 Answers

SOURCE: Running light problem on chevy express 3500 box van

Vehicle electric trouble shooting is the worst. Some of the problems you described the bulbs may have multiple filiments with only some burned out. It may sound silly but change the bulbs. Get a couple of new bulbs and try them in the different spots. Time, road vibrations and spring pressure causes the contacts on the bulbs to wear until they get a poor connection then you get a little arcing that build up a residue and a bulb that test good doesn't work.
Your on the right track with the ground wire. Try a test lamp with a good gound connection and test the different sockets, if your test light works but your bulb doesn't you have a ground fault. If neither work check the switch and fuse before you start tracing the wiring. These are just general trouble shooting tips It's very hard to trouble shoot electrical problems sight unseen.

Posted on Jun 13, 2010

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1 Answer

1990 gmc ihave all my lights butback rear driving lights is this the light switch


All your lights and brake lights and turn signals go through the turn signal switch. It jobs is to divide the lights turn signals and brake lights. One can test if the lights are going into the switch and out through the same connector where the turn signal switch comes out of the column.

Nov 04, 2012 | 1993 GMC Sierra K1500

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1998 gmc sierra-no brake lights,bulbs ok,new brake switch,possible wiring?? Help


Try this possibilities to locate the fault. First get your voltmeter or 12v test lamp out. Check the 30 amp Brake (#2) maxi fuse in the under hood junction box.Fuse should have 12v at both sides at all times.
If okay proceed.
Go to the brake light switch. The orange wire should have 12v at all times. The white wire should have 12v when stepping on the brake.
If okay, proceed.
Next thing is the brake lamp relay in the underhood fuse box. Swap the relay with one that looks just like it and recheck the brake light operation. If the relay is no good replace it.
If the relay is swapped and still not working, see if you can feel the relay clicking when someone else steps on the brake pedal.

batt is power from the maxi fuse 12v all times
sls is the white wire from the brake switch 12v with brake applied.
gnd is body ground 0v all times
mfs goes to the multi function switch 12v with relay activated
the circuit is simple—power from the brake light switch white wires turns on the relay which then sends power back to the multifunction switch for distribution to the rear lights.
if you jump terminals batt and mfs the brake lights should come on.
If you have no power at terminal sls with the brake applied then you have a wiring fault white wire between the brake light switch and the relay
Thanks. Keep updated for any more query. You can rate this solution and show your appreciation.

Aug 17, 2010 | 1998 GMC Sierra

1 Answer

Brake lights dont work, replaced switch, checked for power, power to switch, power to fuse, checked wiring to back end, all appears to be good, put power to white wire, no brake lights still, i need some...


You hit it on the nail, you have check every thing we would have checked here at my repair shop, it's going to be the turn signal switch, as you now the brake light circuit run's through it and more then likely your center top brake light works.Bad switch (turn signal).

Jul 07, 2010 | 1991 GMC Sierra

3 Answers

Wiring diagram for 1996 gmc sierra brake asembly


The brake light switch is at fault. Get a new one and replace it. The location is at the brake pedal area mounted on a bracket with a plunger stud that rest on the brake pedal's arm the pad is attached to

May 08, 2010 | 1996 GMC Sierra

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My brake lights have stopped working. The high light above the rear window works fine and the rear signal lights are ok, too. I have replaced the bulbs and ckecked the fuse. Could it be the switch on the...


Hello,
The rear turn signals are wired through the Multifunction switch also called the turn signal switch. The Hazard switch is in that switch also and thats the circuitry the brake lights go through. You need to confirm voltage at the White wire off of the brake light switch and if its ok you have a bad multifunction switch.

I hope this helps.

Roy

Nov 17, 2009 | 2003 GMC Sierra 1500

1 Answer

My trailer wiring on my 2001 gmc sierra works i just dont have brake lights. all the lights on the truck work. its a 7 pin factory install ive never had problems until now. ive checkd all the fuses and...


First replace the trailer light brake/turn signal fuses. I have seen where the fuse will show good, but loose connection in the block. You can easily do it by using the flashers. Using a test light you can check power in and out of the fuse. Just touch the tester to the metal pin on top of the fuse... on both sides. Power in and power out. If power is there on both sides and still nothing below the fuse box, the box is bad. Not a common problem. Also check http://www.etrailer.com/faq-wiring.aspx.

Oct 09, 2009 | 2001 GMC Sierra 1500HD

1 Answer

No brake lights, or no signal lights


brake lights and turn signals work off the same curcit, it could be the fuse or the brake light switch !!!!!!

Jun 05, 2009 | 2000 GMC Sierra

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Factory radio wiring color codes


Here ya go. enjoy!
2002 GMC Sierra C1500 Car Radio Wire Color Codes
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black/White
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: Under the center console.
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

May 14, 2009 | 2002 GMC Sierra 1500

1 Answer

1993 GMC Sierra 4x4, no brake lights, no rear running lights


If you still have this problem maybe this will help. I had to replace the trailer plug on a 93 GMC Sierra K1500 and had a problem with the light's not working. Had to trace wires from trailer plug up to tail lights. The problem was a broken ground wire. It took longer to remove all the tape and replace it than fixing the problem.

Dec 15, 2008 | 1993 GMC Sierra K1500

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