Hi Guys,
decided to pull the blinker relay. It's separate from the hazard-switch and easily pulled from under the dash. partnumber is bosch 0 335 200 007 (see pictures from 5 to 1). I am going to look at it under a good light, but maybe it's best to look for a new one anyway.
I also found out that the mysterious under-dash light, which I now found out to come on whenever the gearbox is engaged, so also when going forward, is supposed to go into a "fasten-seatbelt" sign. Mystery resolved
Thanks for the help!