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Pelican Guest Technical Article
Permission to publish this article is provided generously by
Robin Sun at www.p-car.com
Be sure to visit his site for loads of 993 info!

How to repair 3rd tail light broken wiring 

Contributed by: Gert Carnewal

Below you'll find the DIY, first an explanation of what we are about to do. 

Drawing #1 shows the cross-section in the original situation. 
Inside the car, the power for the 3rd brake light is fed via two black wires which are hidden behind the rubber window seal. The yellow part in the drawing are the two copper conductors which are embedded into the rear glass. On the inside of the car, the two incoming wires (+ and -) are each soldered onto one conductor which takes the power to the outside of the car. On the outside, the two connectors for the 3rd brake light are soldered onto the conductors. 
 


Drawing # 2 is the same cross section but where one of the two embedded conductors is broken. Resulting in a voltage interruption.
 

Drawing #3 shows how to repair the broken conductor. 
You have to bring the wire from the outside, through the rubber seal and connect it to the incoming wire on the inside. By doing so, you "override" the broken conductor. Although the 3rd brake light housing and the outside rubber seal already prevent water leakage, it is better to apply some sealing compound where the wire enters the cabin.  DIY: 


Step 1: Remove the cover of the 3rd brake light. Gently pull upwards. No tools needed. 

Step 2: Remove the 2 nuts with the use of a 10mm socket wrench 

Step 3: Remove the 3rd brake light housing. 

Step 4: Remove the rubber seal in the middle, where the brown and black wire are.  Step 5: Locate the broken conductor. In most cases, the broken conductor is visible from the outside of the car. If you don't find it, do a continuity test between the incoming wires (soldered to the conductors) and the connectors of the 3rd brake light. Of course, you can always repair both conductors. 

Step 6: From inside the car, remove the rubber seal. Make a small hole in the window sealant. This works best with an awl or a small screwdriver. 

Step 7: Cut off the wire on the outside.  Cut as close as possible to the glass to keep the maximum wire length. Strip about 1" of the wire insulation. Tin plate the wire with the soldering iron.  Take a small set of pliers and push the wire from the outside through the hole you made in the window sealant. Use some duct tape on the side of the roof so you don't damage the paint. Once the wire is through the sealant, cut it off so there is only 1/4" uninsulated wire. Solder this wire onto the incoming wire. Don't solder onto the conductor.  Solder the wire onto the top of the incoming wire. This, to avoid heat dissipation on the rear glass. 

Comments and Suggestions:
Pedro Comments: Just one comment on how I solve mine. On the drawing look into the broken conductor. If that's what is causing the open it was in my case you just need to shorten it. I used a wire to connect both parts. No need to drill inside out. Just a simply short.
May 11, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
pp000830 Comments: Great article! Here is some additional info describing how to identify which wire is broken:

Make sure the fuse is good and the tail stop lights are working normally.

Remove the high mounted stop light cover. It is held by clips and just pops off.

You will see the plug connections to the lamp under the cover. Unplug the brown wire and attach the end leading to the lamp to a known good chassis ground and the black wire leading to the lamp to a known good hot + connection on the car. If the light is good it will illuminate.

The brown wire leading from the lamp goes to chassis ground using the rear glass unit to pass the wire to ground. It uses the same grounding wire path as the rear window defogger.

The black wire from the high mounted light is the hot wire that powers when you step on the brake. It passes through the glass unit as well.

To check the black hot wire connection make sure the black wire is plugged in on the high mounted lamp fixture as you found it originally. Unplug the brown wire from the light fixture. Ground the brown wire leading to the lamp, not the wire back to the glass, to a known good chassis ground and press the brake peddle. If the tail lights illuminate but the high mounted light does not the hot black wire is broken, likely in the glass unit. This was my experience.

To check the brown wire connect the high mounted brown wire plug as it was originally connected in the light fixture and unplug the black wire and attach the black wire leading to the lamp, not the wire back to the glass, to a known good battery connected hot + point on the car. If the lamp does not illuminate the brown wire is broken somewhere along its path into the car.

Also in my case I was concerned about damaging the glass or wire abrasion leading to a grounding short by passing the wire through the window sealant.

Here is how I routed the wire:
Under the gasket I drilled a small hole into the steel body passing the wire through the hole to between the roof and the interior headliner. I then passed the wire through the edge of the headliner along the inside window frame. At this point I cut the existing inside soldered wire connection to the glass at the top center edge of the inside glass surface and attached the new hot wire leading from the existing wire in place along the top glass edge.
I used a razor blade to gently release the existing wire’s insulation from the glue holding it in place to attach in the new replacement wire.
To avoid leaks and protect the new pass-through replacement wire I used 3M automotive weather-strip adhesive, the yellow sticky snot like stuff to seal things up. Once I placed the adhesive I worked the replacement wire in and out of the hole in the steel so the adhesive would fill the hole and immobilize the pass through wire so it would not vibrate and abrade against the edges of the hole minimizing the potential to short out at some future time,
April 30, 2009
  Followup from the Pelican Staff: Great additions, thanks for the input! - Wayne at Pelican Parts  

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