Trailer connection E290

Hello Group,
A friend of mine connected a Swedish trailer to his 1997 E290 T wich he bought in Germany. Whith the turnindicator to the left the trailer blinked
right. He decided not to use the turnindicator, but after a short time the "ESP" and "ABS" came on and they wont go off now.
I have a -92 300 TE bought in Germany and Ive connected a Swedish trailer with no problem what so ever.
My friend is now on his way to a MB-shop to turn off the warninglights but Im sure this group knows more about our MB-s than most MB-mechanic in Sweden. Please respond ASAP.
/Peter, Sweden
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