Perhaps this will be of some interest to anyone with an SL. Mine is a '94.

This happened to me last year. While driving with a friend behind me, when we reached our destination, he informed me that my 3rd brake light was inoperable. I disagreed with him because none of the idiot lights had illuminated. Lo and behold he was right.

When I got home I started checking. To make a long story short, I found in the owner's manual a sentence saying that there was no indication in the dash if the 3rd brake light was out.

Upon checking, I found the problem. In the wiring at the lip of the hood, near the rear window, it had broken. I had to take off the covering from the trunk lid and splice the two wires together, which were covered in a sheath.

I do hope this helps anyone who finds their 3rd brake light inoperable. Remember, there is no visual warning in the car. To check it, of course, have someone stand behind while you press the brake (of course you'll need to turn the key).