There is relay which I think is the fuel pump relay under the drivers seat. The stock wiring harness goes there and it doesn't look as if it had ever been modified by some short-circuit-electrician. It is simply hanging loose under the carpet. To replace it one would have to remove the seat and a lot of mouldings in order to have access to under the carpet. No worse location possible for it imo. Yesterday I unplugged this relya from the socket just for curiosity and replugged it. Did the same this morning and found a connector bent. Straightened it, plugged it in and everything is working ok now. Will check for the inertia switch anyway, am curious where it is and how it looks.
Thanks a lot for Your help, gentlemen, I can go and finish my carpet job now, good sunday job, no noise.