I just got the single red T flashing on gen2 charger today for the first time. Here's my story:
Purchased a 2013 P85 in Oct 2013. No problems charging on a 14-50 plug at my old house or new one for 5yrs.
Get a loaner P100D MX, bring it home... Won't charge using my gen1 charger. Starts to charge, but the breaker flips as it goes through its test. I call customer support and I want to say they walk me through a procedure (this was months ago so I can't remember what that procedure was) and it starts working.
Turn the MX loaner back in, months go by no issues with my p85 on its gen1 charger.
Then I get a MS P100D loaner, bring it home to charge... Same issue. Call customer support. They have me shut down / power off the car. Try to charge. Breaker flips before amps ramp up. Never could get it to charge at my new house. Keep in mind new house has TWO 14-50 plugs one that gets used the other not used at all. Both plugs same behavior. Breaker flips when charging begins before amps ramp up (during it's testing cycle). P100D MS loaner came with gen2 changer. Try it. Same behavior on both plugs... Breaker pops.
Turn that one back in and was never able to get it to charge on either plug using original gen1 or new gen2 charger... Sell my 2013 p85.
Fast forward few more months... 100D loaner i'm thinking about buying. Same problem. This time I decide to research.... Stumble on some threads saying that GFCI breakers can be the issue?? Um, why would all the sudden BOTH plugs have the same issue, particularly considering the theory on these threads is that the GRCI breaker is wearing out and going bad. Well, they are only two years old and one was never used.. both flipping? Hmmm... my electrician comes out and we swap one of the reakers to the original 50a breaker without GFCI... 100D charges like a champ several days no issues... Get home today... Blinking red T on mobile connector. Red light on charge port. I'm thinking... Well this is new. breaker hasn't tripped I still have power but it isn't happy. Dash screen gives some type of message that makes me wonder if I should unplug the gen2 charger and replug and try again. So I unplug from car, unplug gen2 charger from 14-50, wait 10 secs, plug it back into the socket, connect to car... Viola. Happy again. WTF?
One thing I can say with pretty strong certainty: when Tesla was on the old onboard single 40a or dual 40a (total of 80a) inverters, I never had any issues. When they went to the new onboard 32/72a chargers, those go through some type of ground or some extra safety check that causes GFCI breakers to trip. Whether that is related to the ground fault error I saw tonight on the gen2 connector where one T blinks red, I don't know... But I suspect they might be.
Long story short, the only way I can charge my new 100D is by using a non-GFCI breaker which is very dangerous in a carport that routinely gets wet... And it's not up to code either. I'd call customer support and try to talk to them about it but I haven't been able to get anyone to actually ANSWER THE PHONE even after calling 3-4x and waiting for OVER AN HOUR before finally giving up. No exaggerating. One of those times it said my hold time would be "over 5 mins"... I waited for 78m exactly before hanging up because I need to go to bed. Unfrigginreal