Appendix “C”: 993 High mounted Cyclops light wire fix

Appendix C
993 High-mounted Cyclops light wire fix

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

Remove the body color painted high-mounted stoplight cover. It is held by friction clips and just lifts 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 the chassis ground using the rear glass unit to pass the wire to a body 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 ground 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 to ground.

Once you find the bad wire you can reroute it to the wiring harness located under the interior rear deck cover panel where the rear speakers are mounted. 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. 

• The preferred and least invasive wire routing is to reroute the

  

  The Preferred Fix

  existing wire to the lamp under the glass by making a hole in the glass sealant under the top center of the glass and passing the wire through it as discussed here https://p-car.com/diy/glass/

• The alternative way I did it years ago was to cut away a small top-center section of the outer rear window surround. Under the surround, 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 a replacement 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 under the rear deck cover.. 

In my case when connecting the replacement hot wire to the car I cut the old connection wire to the glass at the top center edge of the inside glass surface and attached the new hot wire to it.

I used a razor blade to gently release the existing wire’s insulation from the glue holding it in place along the edge of the glass to splice in the new replacement wire. By doing this I avoided running the replacement wire all the way down to the stop light harness under the deck cover 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 new 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,

10/2022 - This repair has been in place on my car for over ten years and has proven to be very durable.

Consider adding a strobeing light function to the high mounted stop light greatly improving awareness for the cars behind you when braking. 

Also, consider adding stop/marker illumination to the rear-facing center reflector to improve visibility from the rear.

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