Left Rear Tail Lights Out, how to find break?

[adrianv]

Any help would be appreciated.  I have 2002 Avalanche and the LR tail lights are out RR work fine.  I see they are on seperate fuses so I checked that (the likely problem).  Checked all the fuses (in under hood box) since I had my meter out... all good.  Pulled the plug where the tail light plugs in at the rear and no voltage on the appropriate pins.  Ground wires are good.

By process of elimination I assume there is a broken wire.  How do I find a broken wire?

Where can I get a wiring diagram for the exterior lights?

Thank you!

Adrian

[Chevalanche]

how are you checking the fuses?also, are you referring to just your running lights, brake light, b/u lights or what? check them for operation in different modes, flasher, turn signal, when you hit the remote etc....know what I mean?

[DougD]

You haven't stated the obvious - bulbs are good?

[Chevalanche]

You haven't stated the obvious - bulbs are good?

man I hope they are......................

[adrianv]

The lights in question are the running lights/ parking lights left rear.  When just the headlights are on, the top two bulbs lower intensity filament should be on constane.  There is no voltage on the correct pin in the socket for the bulb but the ground is good.  

Each fuse was checked for continuity with a multi-meter.

Thanks, for the bulb suggestion, I am hoping it is that simple.

Maybe the left and right sides run on seperate relays or have subfuses down line?

[Chevalanche]

check down near the trailer harness junction, make sure everything is still tight. check at the trailer connector  and see if you have power there. Are you checking the fuses while they are in the block or out?  One of these gurus on this site has schematic access that I would give my left arm for. Hopefully one of them will cjhime in with that info.

[ShapeShifter]

Maybe the left and right sides run on seperate relays or have subfuses down line?

Yes, there are multiple fuses controlling the rear lighting.

For 2002, the parking lights circuit starts in the under hood fuse block, with the 30 amp "PARK LPS" fuse. It then passes through the parking lamps relay that is in the relay block down by the driver's left foot. From there, it goes back under the hood, where it then splits off into several circuits:

• Under hood "FR PRK" 10 amp fuse:
  • Left front side marker lamp
  • Left front park/turn signal lamp
  • Right front side marker lamp
  • Right Front park/turn signal lamp
• Under hood "TRL PRK" 15 amp fuse:
  • Trailer plug park lamps circuit
• Left dash "INT PRK" 10 amp fuse:
  • Interior door switches
  • Ash tray light
  • Glove box light
  • Radio
  • Many other interior lights...
• Under hood "LR PRK" 10 amp fuse:
  • Left license plate lamp
  • Left park/turn lamp
  • Left tail/stop lamp
• Under hood "RR PRK" 10 amp fuse:
  • Right license plate lamp
  • Right park/turn lamp
  • Right tail/stop lamp

I was going to post wiring diagrams, but this is all spread over about 10 pages, and that's just too much to scan. Also, keep in mind that this is just the low intensity parking lights function we are talking about here. There are even more fuses, and twice as much wiring involved in the higher intensity stop and turn functions.

From this, I would bet most of my money on the "LR PRK" fuse under the hood. Make sure that fuse is working. If your meter says the fuse is good, and there is power being supplied to one side of the fuse (meaning the internal wiring of the fuse block is good) then I will look more closely at the wiring diagram and give more ideas of where to look to try to isolate a break. Also, if that fuse is good, are both of the license plate lights working? There are several connectors these circuits pass through, and knowing exactly which lights work and don't work will help narrow down the problem.

-- SS

[adrianv]

Thanks for the replies.  Yes, I have power as far as the "LR PRK" 10 amp fuse under hood.  

Good news though, after driving it this way for a week it decided to work tonight and is visibly flickering.  So now I will get under there and wingle things around while the wife watches the lights.  Thanks for the license plate lamp tip, did not know they were on the same circuit.  

 

[ShapeShifter]

Yes, I have power as far as the "LR PRK" 10 amp fuse under hood.

OK, so if there is power getting to that fuse, the fuse is good, and the bulbs are good, it has to be something in the wiring. My guess is a connector contact is loose or corroded. Your flickering symptom seems to also indicate that.

Attached is the wiring diagram for the tail lights. Click the blue paperclip link to see it full size. On another page, it shows the LR PRK fuse in the under hood fuse block, and it shows the circuit passing through a connector on the back of the fuse block. (Let's hope it's not there, for now.) From that connector, it shows the circuit going off page with the "M" label.

On this diagram, the circuit then comes in with the "M" label, passes through Pin G of connector C405, then through pin E of connector C402, then splice S417, and on to the lights. So, it looks like either a wire is broken, or there is a bad connection at C405, C402, or S417.

If the left license plate light works when the left tail light doesn't, then I would guess the problem is at or near C402. If the license plate also doesn't work, then the problem is probably at or near C405.

C405 is an inline connector near the left rear corner of the truck. It should be blue, and appears to be sealed. If you climb under the truck you should be able to see it near the frame rail. (At least that's what the book shows.) The brown wire (not the brown/white wire) is the parking lamps circuit. Disconnect this plug, check for clean contacts, and try measuring voltage there.

C402 is an inline connector near the left rear tail lamp. This is a grey connector, and I have seen it when I replaced my tail light assembly, so I know right where it is. If you remove the tail lamp (open tailgate and remove a couple screws) you will see a foot or so of wire attached to the tail light sockets, and then the C405 plug. The brown wire is the parking lamps circuit. Disconnect this plug, check for clean contacts, and try measuring voltage there.

If that does have voltage, then maybe splice S417 is open. This is a splice inline in the wires between the connector and the tail lamp sockets. If the break is there, it should be relatively easy for you to find and fix it.

If none of these have voltage, then it is either in the big red connector under the under hood fuse block, or there is a broken wire somewhere inside the harness under the truck. The left parking lights circuit leaves the fuse block in the red connector, on pin B1. This is a brown wire with no stripe, which is next to an orange wire. There is one other brown wire, but this is the trailer parking lights, and does not have an orange wire anywhere near it. There should only be one orange wire on the red connector, so that should make a good marker for the correct solid brown wire.

If you need any diagrams of the individual connectors, I can supply them, but it should be sufficient to just look for the brown wire.

Good luck!

-- SS

[adrianv]

Thanks for the wiring layout.  Well, I pulled the spare tire, and with the wife watching the now working lights, I started shaking the wiring harness starting at the LR tailight, when I got all the way across the truck to the RR where all the harness plug into different sockets on the frame the lights flickered more off and on then went out completely so it must be in one of those plugs.

By the way, neither of the license plate lamps work, I did not check the bulbs but assume it has to do with the short.  

I looked at AV and love it (mines exactly the same).  Looks like fun with the club cruises.  If you ever cruise to Glacier Park in Montana I'll tell you my favorite spots.

Thanks

[Rangerfan]

You haven't stated the obvious - bulbs are good?

I wouldn't think it would matter if there is no voltage to them.

[Chevalanche]

The question that I have is "how " are you checking the fuses? With a multimeter in the DCV mode, you should be reading battery voltage on both sides of the fuse. Is this the case? Don't do a continuity check on the fuse while it's in the fuse  block. Take it out to check it this way. You can actualy read back through the circuit and think that you are reading a good fuse when it's bad. With me on this?

[adrianv]

Thanks again for the repleis.  I had no voltage at the tail light because of a loose connection.  I have not located the actual spot yet but it appears to be on the RR where all the plugs plug into a panel.

I will no more at the end of the day.

You are right on checking the energized fuses, pulled the suspect one and checked it and even swapped it out.

[adrianv]

Just in case anyone was curious, it wasa broken wire, where all the harnesses plug in at the RR of the truck.  License plate lamps were alson out but due to bulbs.

Thanks for the responses.

[sperry]

The 03 has a connector on the left side, near the end of the frame. Did you see one in the 02?

Here's a print:



You'll need to click on the pic or link to expand it, Much mo' bigerer and clear too..

HTH!

[adrianv]

On my o2 the connectors plug into a panel on a frame rail just behind the RR (passenger side) tire.  Poor place for connectors considering all the magnesium chloride they use on the roads around here.  Probably why it was broken.

[DynoTechJim]

you guys have been a great help saving me time and $ figuring out why my left rear running/ parking lights were not working. Zero juice at the brown wire going to the final connector before the L tail light, and 12v juice at the brown wire coming from the blue plug by the RR wheel. so instead of trying to find the break inside that rat's nest, farmer Jim just ran a jumper wire from the blue plug to the same brown wire just before that last connector before the L tail light. Goobered the splices with silicone to keep the salt away, and all is good (except I still don't have a left side license plate light, but one seems plenty). thanks for the help!

[ohiobellboy]

you guys have been a great help saving me time and $ figuring out why my left rear running/ parking lights were not working. Zero juice at the brown wire going to the final connector before the L tail light, and 12v juice at the brown wire coming from the blue plug by the RR wheel. so instead of trying to find the break inside that rat's nest, farmer Jim just ran a jumper wire from the blue plug to the same brown wire just before that last connector before the L tail light. Goobered the splices with silicone to keep the salt away, and all is good (except I still don't have a left side license plate light, but one seems plenty). thanks for the help!

Check for a broken ground wire to fix that LP light.

[RENORCR]

There's also a Junction Block mounted at the right rear passenger fender above the muffler.
Common moisture issues.

[ohiobellboy]

There's also a Junction Block mounted at the right rear passenger fender above the muffler.
Common moisture issues.

That's been mentioned a few times already. 

[joecool122273]

I have a 2004 with the same problem . i am not getting voltage to the 10 amp fuse LRPRK in fuse box under hood. I have power back at the blue connector behind right rear wheel . How is power fed to the LRPRK fuse under the hood  ?