Tacho not working and Low oil pressure warning

[Steve770]

So the night before setting off on my planned NC 500 trip in the S2 I was driving to go get some fuel and the tachometer stopped working!
To set the context I fitted a stereo the day before where I tapped a wire from the ignition switch for a switched live (the thin red wire). While here I got a big inquisitive and disconnected the three connectors at the back of the Instrument cluster including the yellow one which I believe has the feed for the tacho as the whole thing was a bit loose. Connected it all back up and everything worked as it should - drove for the rest of the day without issue.

Next day I topped up the oil, packed the car and went to get the fuel and that's when the issue started. As soon as I got above what would presumably be 2k rpm the red oil light comes on with the accompanied beeps. Stop the car - took the under cover off and then everything started working again for about ten minutes then same issue. Left it for the night and tried again in the morning - again worked fine for about 10 minutes then the same problem again. It is now no longer intermittent and happens every time I start the car.

The needle is not completely dead - when at idle it sits at 700rpm - but when revving it goes down instead of up!

https://streamable.com/xafcd

It seems as if it's receiving the correct reading from the engine at idle but more revs are causing it to lose signal(?)

I've removed and reseated the connectors and tried to see if I've disturbed anything else when I was there but all looks good. The fact that it's not completely dead and that the oil pressure warning light is triggered after 2k rpms (not during autocheck) has me puzzled. It seems too coincidental that I remove connector literally directly behind the tacho the day before and that not be the issue - though it working fine initially and gives me a little doubt.

To be totally honest I'm not really sure what I'm doing with electrical stuff so feel like a bit of an idiot for messing about in the first place. In the end I took the 80 V6 on the NC500 instead as the thing seems literally bulletproof.

So to summarise the tacho sits at 700rpm with occasional dips to zero and always goes to zero when increasing the revs.
After about 2k rpms the oil pressure warning light comes on.

Any advice on what to check (baring in mind I don't really know what I'm doing) or any experience would be great! I did read a similar thread on here with a similar issue - thought in that case the tacho wasn't working at all.

Thanks in advance!
Steve

[Roach]

I would diss connect the wire for the radio first and see if it makes any difference

[Bowie69]

The oil warning is engine speed related, so I think that is a secondary symptom of the rev counter not working properly.

It has gone a bit funky hasn't it

I'd be tempted to re-seat the connectors on the bulkhead for the engine speed/position sensors.

Other than that, read the codes?

[Mikes2]

Wiring diagram is here : http://s2-audi.co.uk/workshop/schema..._aby/page8.png . pin 22 is a green / blue wire of the yellow connection on the rear of the cluster. That is your vehicle speed signal which goes to the ecu pin 40 (lilac wire). pin 23 is brown / black and goes to earth - make sure those 2 wires are not touching each other. Check for a short between pin 22 and earth

It did this to me once but it never happened again so I'm not convinced that fitting a radio has made a difference

[Steve770]

Cheers guys - apologies for the late reply - it seems to have resolved itself and didn't want to jinx it!

Mikes2 Cheers for the info Mike. I think you're right about the radio - it now seems to be back to normal. Went out armed with the diagram you linked to get stuck in a few weeks ago, started it up and working fine! No sign of it again after a few weekend drives - fingers crossed Don't really want to go poking about while it's working but all the wires look good. Tome will tell I guess.

Thanks again