my break lights dont work like they should

1990 GMC C1500
173,550 MILES • 4.3L • V6 • 2WD • MANUAL
Avatar
KEEGANLILES
  • MEMBER
  • 16 POSTS
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.
Mar 18, 2014 at 9:28 AM
Advertisement
Avatar
JDL
  • CERTIFIED EXPERT
  • 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?
Image (Click to enlarge)
Attached Media
Mar 18, 2014 at 12:03 PM
Avatar
KEEGANLILES
  • MEMBER
  • 16 POSTS
Yes we are getting 12volts
Mar 18, 2014 at 12:23 PM
Advertisement
Avatar
JDL
  • CERTIFIED EXPERT
  • 16,098 POSTS
In that case,I'm thinking it's the ground. You could run a redundant ground, see if it helps anything?
Mar 18, 2014 at 12:34 PM
Avatar
KEEGANLILES
  • MEMBER
  • 16 POSTS
Where should I run it from&to?
Mar 18, 2014 at 12:49 PM
Avatar
JDL
  • CERTIFIED EXPERT
  • 16,098 POSTS
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.
Mar 18, 2014 at 12:56 PM
Avatar
KEEGANLILES
  • MEMBER
  • 16 POSTS
But t try he breakpoints coming on and off at the wrong time is the switch but the switch is brand new.
Mar 18, 2014 at 1:13 PM
Avatar
JDL
  • CERTIFIED EXPERT
  • 16,098 POSTS
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?
Mar 18, 2014 at 1:35 PM
Avatar
KEEGANLILES
  • MEMBER
  • 16 POSTS
No it's only when the pedal is not depressed because the switch is backwards like it works opposite of how it should.
Mar 18, 2014 at 1:53 PM
Avatar
JDL
  • CERTIFIED EXPERT
  • 16,098 POSTS
Without being able to look at it, I don't know anything else?
Mar 18, 2014 at 2:08 PM