My 2012 tC RS7 is showing some weird codes and doing weird things.

first the codes, P0793 intermediate shaft speed sensor code is showing i have a replacement but can't find where it goes. it must be in a different spot then a tC1.

second the P0500 code is showing along with the ABS, brake and slip warning lights.

third when I turn on defrost and the brights are on the car dies. Pretty sure its not a battery or alternator prob because that's the only combination it happens in...

when i turn on the brights all a bunch of warning lights flash mostly abs, break and slip warning. Do I have a bad ECU or something? HELPPPP

here is a vid of whats happening with the car turning off