1999 Chevy S-10 High Mount Brake Light

Tiny
KEITH MCGEE
  • MEMBER
  • 1999 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 90,000 MILES
My high mount brake light is not getting power. I have checked fuses, swapped relays, replaced bulbs and checked connectivitiy from the battery to and over the fuse. My lower brake lights come on so I don't think it is the brake light switch. My multimeter does not register any voltage at the light. Does any one understand how its wired so I can do some more troubleshooting? It worked last year and the only thing that has happed since then is I have had the battery and alternator replaced.
Tuesday, January 13th, 2009 AT 2:01 PM

13 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
The high mounts are on a different fuse under the hood on the left fender, check that, and the bulbs, then test the white wire that comes off the stop light switch.


https://www.2carpros.com/forum/automotive_pictures/62217_S10a_1.jpg



https://www.2carpros.com/forum/automotive_pictures/62217_S10b_1.jpg

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Tuesday, January 13th, 2009 AT 2:20 PM
Tiny
KEITH MCGEE
  • MEMBER
  • 10 POSTS
You're going to have to be a little more specific. What and where is the stop light switch? Is that the brake switch under the dash? I have already checked the fuses under the hood and checked the bulbs. Where is the white wire to be found? I took the dome light off and looked at the wires behind the high mount box and I only saw a black and light beige wire there.

I disconnected the rear view mirror light months ago and the wires are just hanging down but my dome light works. Could this have anything to do with it?
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Tuesday, January 13th, 2009 AT 2:29 PM
Tiny
MERLIN2021
  • MECHANIC
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Yes the stop light switch is at the brake pedal, and there should be three wires, the white one powers the high mount brake lights. It runs to the fuse box under the hood, and turns light blue to the high mount. Re connect ALL wires you may have disconnected, and you might solve the problem. The stop light switch may be OK for the regular brake lights, but burnt out for the high mounts too, check the white wir while appling th brake, should get 12 volts.
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+1
Tuesday, January 13th, 2009 AT 6:11 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Have you check the CHML fuse 10amp and also the stop lamp relay in the underhood fuse block

Your power comes from the stop lamp fuse 20amp but it need to get thru the CHML fuse 10amp to get to the high mount/dome light
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Tuesday, January 13th, 2009 AT 6:37 PM
Tiny
KEITH MCGEE
  • MEMBER
  • 10 POSTS
I checked the wires at the light and got no connectivity with the brake depressed, but I got 8.8 volts. Not enough to activate the lights. Is is possible to get a "no complete circuit" reading but still read some voltage like that? Possible short in the wires leading from the light to switch? If I understand correctly the white wire goes only from the fuse box to the brake switch and the lt blue wire goes from the switch to the light. And the black wire from the light is the ground. Is this right? All I did on the rear view mirror was disconnect it, but according to the diagram it appears the dome light and high mount light are on the same circuit. Is that right? Yes I have swapped the relay circuit with the horn and it did not solve the problem.
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Tuesday, January 13th, 2009 AT 7:54 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Did you check the Veh CHMSL fuse 10amp-when this fuse blows you won't have power on the light blue wire on the the high mount brake light.

Inspect the trailer wiring could be causing the problem


https://www.2carpros.com/forum/automotive_pictures/12900_exterior_light_circuit_1.jpg

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Wednesday, January 14th, 2009 AT 4:17 AM
Tiny
KEITH MCGEE
  • MEMBER
  • 10 POSTS
I can't read the diagram. It's too small. Besides, I don't have a trailer and have never tried to wire one up. I have checked the fuses and relays. All of them. My mulitmeter reads 20 on the relays so I guess it's good. I went to a local auto electric repair shop and asked the mechanic about the brake switch. He said if the brake lights work there's no way it could be the switch because the high mount is wired into the same place.
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Wednesday, January 14th, 2009 AT 2:20 PM
Tiny
RASMATAZ
  • MECHANIC
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My mulitmeter reads 20 on the relays so I guess it's good.

What reading is this? -Is it amps, ohms, or volts give me your email address and I'll send you a clearer diagram.
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Wednesday, January 14th, 2009 AT 2:47 PM
Tiny
KEITH MCGEE
  • MEMBER
  • 10 POSTS
Keith1126@gmail. Com
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Wednesday, January 14th, 2009 AT 4:03 PM
Tiny
RASMATAZ
  • MECHANIC
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Brake light circuit sent--
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Wednesday, January 14th, 2009 AT 5:10 PM
Tiny
MERLIN2021
  • MECHANIC
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Pobably the same diagram I posted, can you rad mine?
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Monday, January 19th, 2009 AT 11:56 AM
Tiny
KEITH MCGEE
  • MEMBER
  • 10 POSTS
I just figured out the problem! I was checking voltage at the light and could not get anything off the light terminals so I was placing my leads on the posts that come up out of the bottom of the box and got 12 volts. Surprise! Why wouldn't the light work? I placed the lead on the brass strip and leaned it against the metal post it was attached to and the lights came on. I realized there was a bad connection between the wire post and the strip so I took a punch and hammer and tapped it back down so it would make contact and my light works fine now. Thanks for your help though. I learned a lot about brake lights and wiring.

Keith
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Monday, January 19th, 2009 AT 10:04 PM
Tiny
MERLIN2021
  • MECHANIC
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Good work!
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Tuesday, January 20th, 2009 AT 4:44 PM

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