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2004 Chevy Silverado Z71 All Brake lights do not function
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Fernie ski bum
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Nov 11, 2015, 1:22 PM
Post #1 of 36
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2004 Chevy Silverado Z71 All Brake lights do not function
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Just realized my Brake light do not work. All three an non operational. The clearance lights, back up, signal, plate light all work it is just the Brake lights. Brake and clearance / marker are the same lamp so I know there is connectivity from front to back. I have pulled the brake light switch out and took it apart to check the contacts none are burnt and when the spring is depressed the two contacts disengage and the one contact to effectively complete the circuit to light up the brake lights engages correctly. I have metered the wires and have 12.8 VDC on the correct wire at the wiring harness which plugs into the switch. I have jumpered the hot wire to the brake wire on the switch wire harness ( traced the connection in the switch and bypassed the switch) to check the connection and still could not get the brake lights to illuminate. So short of going to a shop I am at a loss. Any ideas on this specific make and model appreciated to either confirm or eliminate the switch or the wiring from the dash to the rear.
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kev2
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Nov 11, 2015, 1:39 PM
Post #2 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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did you check fuses?
check if fuse gets12v when depressing brake pedal?
thinks to consider - is there a tow harness? rear plug in taillight connector.
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Fernie ski bum
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Nov 11, 2015, 1:55 PM
Post #3 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Maybe I am not clear, there is power at the wiring harness so there must be power at the fuses,correct?Yes there is a factory trailer harness.
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Fernie ski bum
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Nov 11, 2015, 1:56 PM
Post #4 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Yes, I have checked all fuses and all are good
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Discretesignals
Ultimate Carjunky
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Nov 11, 2015, 2:10 PM
Post #5 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Clearance lamps do not share the same circuit as the brake lamps. Running and brake share the same bulb, but different filaments.
Do you have good power and ground at the brake lamp connectors?
Light blue wire is the brake lamp feed circuit at the brake lamp socket. Black wire is the ground.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 11, 2015, 2:18 PM)
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kev2
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Nov 11, 2015, 2:10 PM
Post #6 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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got to start somewhere so-
ck the fuse in underhood 25amp stop fuse,
ck orange wire at brake switch 12v,
ck left dash fuse box .'veh stop fuse' 15a- only has 12v when stepping on brake yes no?
ck brake bulb circuit ltblu wire is there 12v stepping on brake?
do not look at fuses check them and depress pedal for in cab fuse ck
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Discretesignals
Ultimate Carjunky
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Nov 11, 2015, 2:18 PM
Post #7 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Sorry Kev....you got this 
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Fernie ski bum
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Nov 11, 2015, 2:47 PM
Post #8 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Will do. Do I need the switch reinstalled to do this to complete the circuit
I am also checking the power at the trailer plug to see if I have power there as well and will report back shortly
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kev2
Veteran
Nov 11, 2015, 3:44 PM
Post #9 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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brake switch must be installed - we are trying to see where power is lacking - going from front to rear.
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Fernie ski bum
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Nov 11, 2015, 3:45 PM
Post #10 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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ck the fuse in underhood 25amp stop fuse,
Fuse visual check is OK Pulled fuse checked for voltage, got 12.4 did not matter if peddle was depressed or not always hot
ck orange wire at brake switch 12v,
Power at wire harness 12.8 VDC
ck left dash fuse box .'veh stop fuse' 15a- only has 12v when stepping on brake yes no?
Reinstalled switch, removed fuse Checked both side of fuse without touching brake peddle no reading, depressed peddle got 12.45 on one side of fuse
ck brake bulb circuit ltblu wire is there 12v stepping on brake?
Checked at rear trailer plug no reading on meter
do not look at fuses check them and depress pedal for in cab fuse ck
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kev2
Veteran
Nov 11, 2015, 4:23 PM
Post #11 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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in cab fuse box 'veh stop' - yes only 12v when stepping on brake. both sides - might want to swap that fuse...
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Fernie ski bum
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Nov 11, 2015, 4:30 PM
Post #12 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Update.I pulled the bulb in the rear light fixture and checked the bulb base. There is 12.45 VDC on the Lt Blue when the peddle is depressed but bulb does not light up. My guess is now a ground issue. Am I on the right path?
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Fernie ski bum
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Nov 11, 2015, 4:36 PM
Post #13 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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To be clear, are you telling me I should have 12 VDC on both sides of the fuse and not just on one side when peddle is depressed? Swapped out good fuse for another good fuse no change in situation.
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Discretesignals
Ultimate Carjunky
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Nov 11, 2015, 5:21 PM
Post #14 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Just a little tip. If you have power to the socket when you press on the brake pedal, take your multimeter and back probe the black wire (ground) on the socket with the bulb installed. Make sure your meter is connected to a good ground. Then take your meter and configure it in the amp mode. Just move your red lead to the amp port.
When the meter is in amp mode, it is basically acting as a jumper. If the light comes on, you have a ground issue.
After your done make sure you move the red lead back to the voltage/ohm port. If you don't and measure voltage with it, you'll blow the fuse inside the meter. You also should make sure the fuse is good inside the meter or this test won't work.
Also don't connect your meter to the blue wire in amp mode or that will blow the fuse also.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 11, 2015, 5:26 PM)
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Fernie ski bum
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Nov 11, 2015, 9:58 PM
Post #15 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Got tied up on an other matter will do this in the AM and report back
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Fernie ski bum
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Nov 11, 2015, 10:29 PM
Post #16 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Tried it no luck, as I was thinking about it the clearance, signal and back up lights all work and are on the same ground wire.
Any other suggestions?
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Tom Greenleaf
Ultimate Carjunky
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Nov 12, 2015, 12:08 AM
Post #17 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Just a note: Ground for everything must be good. Truck bed isn't grounded without straps to do so + may be a couple. Add as needed. All powered anything must make it back to battery negative - got it?
What was with that fuse that had power to one side + not the other? New blow right away or stay good? Sounded like that was your problem or the clue?
BTW- I think trailer lighting is totally separately wired but could interfere only. Clearance lights not about this on cab........
T
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kev2
Veteran
Nov 12, 2015, 7:38 AM
Post #18 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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you have the problem isolated- there is 12v at ltbl wire- your test light will light selecting independent ground so bad bulb or bad ground...
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Fernie ski bum
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Nov 12, 2015, 9:02 AM
Post #19 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Don't understand your comment on Ground? When I checked the ground I used the frame of the truck to check not the box. If all other lights in cluster in the rear share the same ground <backup, marker, plate> and they all work then should the brake light also work?
Yes, I understand the negative must make it back to the battery. That is why I tested everything to the frame.
When I checked the fuse connection I pulled the fuse and checked the connectivity on each side of the fuse connection not knowing which side the power is coming from. No fuse has ever blown. So, as I understand the fuse wiring, there should only be power to one side of the fuse so if the fuse blows it acts like a switch and cuts power down stream or am I missing something?
There is a plug block in the rear of the truck mounted on the frame behind the bumper. There is a wire bundle from the front of the truck that plugs into it with all the signal wires and ground. Prior to that wire bundle plugging into the block there is a splice of wires that feed directly into the trailer plug. From the wire block three wire harnesses plug in, 1 for the plate lights and then the left and right rear light assembly feeds. I thought because the trailer plug was connected to the front and not through the block I would get a reading, I got nothing but I get a reading at the bulb plug.This is driving me nuts it has to be something simple I just can't find it.
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Tom Greenleaf
Ultimate Carjunky
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Nov 12, 2015, 9:22 AM
Post #20 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Sorry if already checked and said but have you taken a brake light bulb out and checked it with a test light with known ground if you use jumper cables all the way to the battery that it has power when empower test light and it will light for ground.
You can use good jumper cables to go from frame to body as a temporary ground.
Things you can count on: Vehicles will use the least freaking wire possible so each bulb doesn't send a wire all the back for ground but would for most positive power.
Straps are those bare braided wire things you find and some seen some not. When lost even if one looks good clean those. Most are not machine threaded, rather lag bolted thru an eyelet.
Plug connectors: Originally should have been smeared with grease by now hard or water got into a plug, one or multi wire connection. Those are trouble spots too to cause hair loss. Other hair puller is plain knowing test light or meter of any sort is really making a connection. Typical test light with alligator clip end on wire can't just go to painted anything and iffy if rusted too.
Just trying to help with what causes things and when testing isn't working and might not know it,
T
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Fernie ski bum
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Nov 12, 2015, 9:33 AM
Post #21 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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Agreed but all three brake light are non functional. I have tested the rear bulbs so that is not the issue. I have not checked the cyclops light in the back of the cab as I have a canopy and don't care if it works or not because you can't see it. Please don't tell me they are interconnected then I have to pull my canopy off the truck to check it.
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Fernie ski bum
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Nov 12, 2015, 9:39 AM
Post #22 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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I really appreciate all the help I feel like I am all alone on this and certainly do not have the answers.You guys are a great sounding board.I will keep plugging away and report back or ask for more advise
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Discretesignals
Ultimate Carjunky
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Nov 12, 2015, 10:00 AM
Post #23 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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The CHMSL bulb could be blown, but without checking there you won't know.
You stated you had 12 volts sitting at the blue wire at the brake/tail lamp socket. Did you check that by back probing the connector or removing the bulb and checking inside the socket?
You should check with the bulb installed and circuit powered up. Then back probe with your volt meter. Make sure you volt meter has a good ground. If you have to, run a jumper to the negative battery terminal to connect your meter neg lead to.
When you back probe the socket with the bulb installed and circuit powered up (brake pedal depressed), the blue wire should have close to battery voltage. The black wire should be less than 0.3 V.
If you are checking a circuit that is open (bulb removed), your not reading the circuit with a load on it and that can throw you for a loop if there is resistance in the circuit somewhere dropping the voltage.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Fernie ski bum
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Nov 12, 2015, 10:18 AM
Post #24 of 36
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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The CHMSL bulb being ( I assume the back of cab light?) Is it interconnected?
I checked the back Brake light lite Blue wire in the socket with bulb out. I will back probe it and report back.
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Fernie ski bum
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Nov 12, 2015, 10:36 AM
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Re: 2004 Chevy Silverado Z71 All Brake lights do not function
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OK here is the 411
All this was done with bake peddle depressed
I put the bulb in the socket and back probed the lite blue wire No reading on meter. Still no bulb illumination
I pulled the bulb and back probed the Lite blue wire no reading
I probed the socket and there is power when the peddle is depressed no reading when peddle is released.
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