EPS circuit

Hello Have again a question to the Daimlerspetzialisten Have a Mercedes-Benz SK,Bj I think about the 1990, chassis number WDB65557315…………. vehicle is deregistered, can not look now exactly what a Bj, but is already with the oblique disc at the door Have problems with the EPS circuit, it is the 6th gear inserted and can only be laid out with the emergency circuit, and after each learning process it automatically jumps again on its own into the 6 gears unfortunately the EPS system can only be read out via the display, it’s the errors 1,2,3,4,5,6,8,8,12,14,16,17 and 18 in the display,if I remember my training that’s what I think short circuits from the control unit according to mass electrical cabling also the under the footboard on the right (was once a known problem) are obviously in order not to think that it’s the gearbox, then several more components should be defective, but I don’t think because until the error everything was ok so only still the control unit or the module in the safety box or the selector lever,unfortunately no one has anything to lie around to test it there is still the possibility to test with the jack box, but is very elaborate and know about it is still such a thing that someone still has an idea? thank you in advance