993 High mounted Cyclops light wire fix
04-12-2009, 04:26 PM
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993 High mounted Cyclops light wire fix
Disclaimer: Use the information below at your own risk. Any adverse outcomes resulting from using the below information are at the information user’s (your) own risk. I am not a professional car technician.
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.
Once you find the bad wire you can reroute it to the wiring harness located under the interior rear cover panel that the rear speakers are mounted in. The entire interior cover panel comes off in one unit and is only held in place by a few screws behind the rear seats.
There are many ways to reroute the wire. On the outside I cut away a small top center section of the rear window gasket hidden by the high mounted light bracket. 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 there are several ways to hide the wire along the window frame to run the wire down to the stop light harness.
In my case when connecting the replacement hot wire to the car I cut the old 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 spliced in the new replacement wire. By doing this I avoided running the replacement wire all the way down to the stop light harness below the window.
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,
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.
Once you find the bad wire you can reroute it to the wiring harness located under the interior rear cover panel that the rear speakers are mounted in. The entire interior cover panel comes off in one unit and is only held in place by a few screws behind the rear seats.
There are many ways to reroute the wire. On the outside I cut away a small top center section of the rear window gasket hidden by the high mounted light bracket. 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 there are several ways to hide the wire along the window frame to run the wire down to the stop light harness.
In my case when connecting the replacement hot wire to the car I cut the old 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 spliced in the new replacement wire. By doing this I avoided running the replacement wire all the way down to the stop light harness below the window.
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,
08-31-2014, 05:01 PM
#4
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Update, August 2014 - fix still working properly.
08-23-2015, 08:01 PM
#6
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10-31-2016, 09:13 AM
#7
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10/2016 still working
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03-27-2018, 06:58 PM
#8
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3/27/18 - still working
10-16-2018, 10:34 PM
#9
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Just wanted to say thanks for this post. Just fixed my car, 1996 C2, following your directions. A couple of things I noted in regard to some other post I saw on the same subject ie upper brake light.
1 The red wire gave me 6.5 volts and I assumed that I had a voltage problem. That is not the case, the red wire is the ground. You can confirm that by continuity with the ground on the battery. The 6.5 volts is return voltage from the tail brake lights.
2 The interior black wire on the solder spot gave me 10.5 volts. This spot corresponds to the exterior black which gave me 0 volts. Hence as you said lost connection within the glass. Testing the brake light directly to the two interior solder points confirmed everything inside was as it was supposed to be. Ran a wire from inside to outside, brake light works perfect. Thanks again.
1 The red wire gave me 6.5 volts and I assumed that I had a voltage problem. That is not the case, the red wire is the ground. You can confirm that by continuity with the ground on the battery. The 6.5 volts is return voltage from the tail brake lights.
2 The interior black wire on the solder spot gave me 10.5 volts. This spot corresponds to the exterior black which gave me 0 volts. Hence as you said lost connection within the glass. Testing the brake light directly to the two interior solder points confirmed everything inside was as it was supposed to be. Ran a wire from inside to outside, brake light works perfect. Thanks again.
