There is an electrical short somewhere causing a bad signal to transmission while headlight on.i have a similar problem with my ford truck except when on turn headlamps on it cuts the power to the fuel pump and ignition lol sadly im still looking for where my bad wire is located.if you find your bad wire you will solve your problem if not its best to go to a dealer or certified mechanic .downside is we all know dealers and mechanics are expensive hopefully you can find your bad wire on your own good luck