Avensis 2012 complicated electric problem

[Larske]

Car is Avensis 2012 1.6 valvematic.

Trailer and its lights were attached to the car, drove 500 meters and then all fault symbols appear on the instrument panel.

When I start the car driving lights off, no warning lights come on. But when I turn driving lights on, all VSC, ABS, Engine fault, etc. symbols and messages appear very soon. And when I again turn off lights, the warning symbols and messages turn off also. If I just idle without driving and lights off, I get no fault codes etc. But if I either turn on driving lights or drive without driving lights, faults appear.

Sometimes when the car idles, it flashes left blinker and brake lights itself, changes idle speed a little bit, sometimes left blinker stays on itself for a while.

When I drive and put on high beam driving lights, then use left turn signal, engine shuts off. And I am unable to start the engine, until I turn off high beam driving lights. Right turn signal works fine. Also, when high beam lights are on, speedmeter is not working. It can also lose power steering sometimes when high beam is on.

Fault codes: C1201, C1241, P1047, U0129, C13AA, U0100

Bad cables? Grounding? Faulty ECU etc.? Where are some typical places that might cause this? I don't even know where to look. Dealer inspected the car for 1 hour and had no clue at all.

I am still able to drive the car "normally" even though almost every electric system is disabled...

[avetoy]

Faulty trailer lights control unit?

Should be located somewhere in the trunk...