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04-25-2013, 04:17 PM
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#1 |
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Registered User
Join Date: Feb 2012
Location: Minnesota
Posts: 16
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'98 no brake lights
Hello all!
Got a weird one here. 1998 K3500 - everything worked fine several weeks ago when I picked it up. Only issue was that the turn signals wouldn't function unless downward pressure was maintained on the hazard switch. Used the "penny trick" as a temporary fix; started looking for a new multi-function switch. Today I noticed that my brake lights weren't working - not even the third (top of cab) brake light. Everything else, including the turn signals, were still working fine. I was also still able to cancel cruise by pressing the brakes (brake switch still good?). Checked fuses, no problems. Checked bulbs, no problems. I stopped at the local junkyard and grabbed a untested (as they all were) multi-function switch. It was more worn that I would have liked, but I was in a hurry to find out if my brake light problem was related. Installed it a bit ago... no change, even had to use the penny again! What few wiring diagrams I've been able to dig up have been useless (too little detail for this part of the system). Without any way of knowing what to test, I'm not sure whether the problem is that the "new" switch had already failed in the same manner as my previous one, or whether there's something else wrong. Any ideas? |
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04-25-2013, 06:30 PM
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#2 |
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Registered User
Join Date: Jul 2012
Location: Tatamagouche, Nova Scotia
Posts: 32
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Re: '98 no brake lights
check that the harniss is grounded to the frame in the back had the same problem and the ground wire was broke off
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04-25-2013, 06:55 PM
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#3 |
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Registered User
Join Date: Jun 2012
Location: melbourne, victoria
Posts: 145
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Re: '98 no brake lights
^^i agree
had problems with my third brake light, turned out to be a broken wire underneath the dash. check the obvious first
__________________
1988 GMC c1500 SWB D/D RHD 5.7L 700R4 |
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04-25-2013, 09:57 PM
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#4 |
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Registered User
Join Date: Feb 2012
Location: Minnesota
Posts: 16
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Re: '98 no brake lights
While replacing the multi-function switch (before, actually) I did a check for broken or rubbed wires under the dash. Nothing jumped out at me.
If the ground at the back of the truck weren't making contact, wouldn't I also be without taillights, rear turn signals, etc? Sure wish I could find a proper wiring diagram for this thing. Feel like I'm stabbing in the dark without it. (Anybody got them and willing to share?) |
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04-26-2013, 03:16 PM
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#5 |
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Join Date: Nov 2007
Location: Tx
Posts: 1,011
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Re: '98 no brake lights
I don't know if these are any better than what you have. They might help.
1998 k3500 7.4 brakes.pdf clearance lights.pdf cruise.pdf exterior lights circuit.pdf lights backup circuit.pdf |
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04-26-2013, 03:22 PM
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#6 |
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Location: Tx
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Re: '98 no brake lights
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04-26-2013, 03:51 PM
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#7 | |
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Registered User
Join Date: Feb 2012
Location: Minnesota
Posts: 16
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Re: '98 no brake lights
Quote:
The Exterior Lights schematic was the ticket. It, along with my trusty VOM, allowed me to quickly eliminate several lingering doubts and get down to the root cause: a bad brake light relay. Everything was correct at its socket... B+ when and where it should be, ground where it should be too. I could even jump the two switched contacts and see the brake lights turn on. And, as you could probably guess by this point, the relay failed bench testing. Looks like I need to grab a replacement. Thanks again! |
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04-26-2013, 06:15 PM
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#8 |
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Registered User
Join Date: Jun 2012
Location: melbourne, victoria
Posts: 145
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Re: '98 no brake lights
those diagrams from dragginmetal should be added to the FAQ's section
__________________
1988 GMC c1500 SWB D/D RHD 5.7L 700R4 |
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04-27-2013, 09:28 AM
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#9 | ||
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Re: '98 no brake lights
Quote:
Quote:
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04-27-2013, 10:13 AM
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#10 |
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Re: '98 no brake lights
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04-27-2013, 10:17 AM
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#11 |
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Re: '98 no brake lights
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04-27-2013, 10:20 AM
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#12 |
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Re: '98 no brake lights
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04-27-2013, 10:24 AM
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#13 |
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Re: '98 no brake lights
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04-27-2013, 10:28 AM
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#14 |
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Re: '98 no brake lights
interior lights cc w-aux lighting.pdf
interior lights cc wo-aux lighting.pdf interior lights instrument 1.pdf interior lights instrument 2.pdf interior lights rc xc.pdf |
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04-27-2013, 10:32 AM
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#15 |
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Re: '98 no brake lights
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04-27-2013, 10:35 AM
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#16 |
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Re: '98 no brake lights
seats lumbar bench.pdf
seats lumbar bucket split bench w heated.pdf seats lumbar bucket split bench wo heated.pdf shift interlock.pdf sound w amp.pdf |
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04-27-2013, 10:38 AM
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#17 |
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Re: '98 no brake lights
sound wo amp.pdf
starting charging 1.pdf starting charging 2.pdf steering.pdf transmissions 4l80e.pdf |
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04-27-2013, 10:42 AM
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#18 |
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Re: '98 no brake lights
transmissions 4wd wo e shift w hd transmission.pdf
warning.pdf windows 2d.pdf windows 4d.pdf wiper washer.pdf That's all of them. |
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