JPP
Active Member
I am also in Southern California. I have tried both styles of transponder (larger square version and the newer rectangular version with the 3-position switch), with no success thus far. I have a 2016 refreshed Model S similar to the OP. I have tried multiple orientations in the black area to the right of the mirror. The only orientation that I have yet to try is upside down - I will try that on my next toll road trip. As @dinkoh mentioned, they will do a plate lookup and charge the account for OC tollroads, but one freeway down here (the 110) makes use of the switched transponder to indicate a carpool. If we are carpooling (to the Rams game ) up the 110 and the transponder doesn't trigger, we will be charged via the plate lookup for what should be a free trip.
Not sure what the rules are in SoCA, but in NoCA I can leave our switchable transponders in #3, for all HOV lanes and paid time-of-use lanes. Since I do not need to fool with the switch, in my wife's S70D where there is no good position that registers in the front windshield, I have mounted the transponder in the bottom center of the rear liftgate window. Invisible as it is blocked by the middle seat headrest. Works great. And if you wonder why it is not mounted in the top edge, that is where the Blackvue rear camera is mounted.