Toggle switch under dash (280SL / 107)
 

I was running some wires for my satellite radio and discovered a toggle switch under the dash, just to the right of the steering wheel. It's out of view of the driver but within arms reach. I toggled it with the car on as well as off, didn't seem to notice anything happening. I was concerned (and kind of hoping) the passenger seat might eject or a smoke screen would come out the back, but that didn't happen either. Any thoughts? Unfortunately I don't have a manual to check. Thanks...

Possibly a "kill switch"? 'Unless switch is in proper position, car cannot be started' was a common anti-theft device, long ago.

Just a guess..

power antenna - up /down, that is what it is in my 72

If it is a kill switch then trace the wires. If the wiring goes to the coil on the negative side then it is a kill switch.

I ran one on a 71 mustang in series with two switches. You had to find both and toggle them in the right positions.