Originally Posted by Red_bull

The fuel relay needs a tacho input on the middle pin to run the fuel pump when the engine runs. So I can't disconnect that one. Do you have the original relay?

Diodes are the right way around, but it looks like I don't see the first 1500rpm or something. Maybe the 15V zener that I took is still too high?

Anyway the problem got more strange
My battery wasn't charging, because my blue connector on the dials was off, so I decided to disconnect the tacho signal to there (as the reading was bad I assumed this caused the problem). Put the blue connector back on and now it kept running again with 5 Volt on it with and without the blue connector.

We started to measure where the 5V came from with running engine and key out and found that the black and yellow wire from the blue connector had 5 volt on it. Traced it down to the fusebox. Brake pedal fuse connected to this one. Started it again, took key out, hit the brake, engine off.

What feedback does the brakepedal send to the dials? The tacho signal present or not present does change the problem. I deff have a problem somewhere in my wireing, but I don't know where.

For now the black and yellow wire is cut and everything seems to work fine. But I would like to trace the problem.