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My break lights dont work like they should

Tiny
KEEGANLILES
  • MEMBER
  • 1990 GMC C1500
  • 4.3L
  • V6
  • 2WD
  • MANUAL
  • 173,550 MILES
When I go to apply the break my break lights turn off and then I do apply the break my interior lights also turn off. Also my breaks are very dim. There are two wires that I connected to my breaks they are both white and one wire is hot there is a third wire hanging down under my dash and I believe it is a ground wire it is black. In addition I don't know if this has anything to do with it but I am getting power to the fuse but not to the switch with the original connection. Anything helps thank you.
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Tuesday, March 18th, 2014 AT 9:28 AM

9 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Faulty grounds can cause some funny issues. Your brake lites are wired through the turn signal switch. Turn and brake use the same bulb filament, just not at the same time. At the brake lamp, yellow wire is voltage and black wire is ground. Did you check the actual voltage reading at the brake lamp wiring?
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Tuesday, March 18th, 2014 AT 12:03 PM
Tiny
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Yes we are getting 12volts
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Tuesday, March 18th, 2014 AT 12:23 PM
Tiny
JDL
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In that case, I'm thinking it's the ground. You could run a redundant ground, see if it helps anything?
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Tuesday, March 18th, 2014 AT 12:34 PM
Tiny
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Where should I run it from&to?
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Tuesday, March 18th, 2014 AT 12:49 PM
Tiny
JDL
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Just a clean part of the chassis/ metal part of vehicle. You may have to clean a little paint. You could track the black ground wire where it is mounted. It could just be the wire and not the contact point. Just make sure the contact point is clean metal.
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Tuesday, March 18th, 2014 AT 12:56 PM
Tiny
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But t try he breakpoints coming on and off at the wrong time is the switch but the switch is brand new.
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Tuesday, March 18th, 2014 AT 1:13 PM
Tiny
JDL
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You already said you had good voltage at the brake bulb, with the brake pedal depressed. If they are dim, I'm still thinking ground.

Do you want to check voltage to and from brake switch? Orange wire to brake switch is hot all the time. When you activate the brake switch by stepping on the brake pedal, the white wire goes hot, carries voltage to turn switch and then to brake lites.

I can't tell from here if your brake switch is adjustable?
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Tuesday, March 18th, 2014 AT 1:35 PM
Tiny
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No it's only when the pedal is not depressed because the switch is backwards like it works opposite of how it should.
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Tuesday, March 18th, 2014 AT 1:53 PM
Tiny
JDL
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Without being able to look at it, I don't know anything else?
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Tuesday, March 18th, 2014 AT 2:08 PM

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