What have I done????

You did not dislodge the temp wire by any chance did you, sounds like it thinks its overheating. Over then that ilde down to your local auto electrican, most likely quicker .
Good luck Pete

DIESEL DAVE

you didnt accidently push the engine warm button on the right hand side of the steering column did you?

just a thought :-)

This is why it pays to have a wiring diagram before attempting anything unless you know what your doing.

Check all the fuses and disconnect the battery for 15 minutes and let the ECU reset itself.

The temp wire at the back of the instrument cluster is in most cases a signal output wire, if you disconnected that wire I doubt it would have an impact on the how the vehicle ran.

You might have to get someone with a scan. tool to check what it is and is not doing.

Check all the plugs under the dash and make sure all the wires and pins are OK.

Make sure you have not pinched any wires if you have removed anything or any trim panels.

Get a copy of the earth points and check, most stuff important have multi earth points.

I cannot remember if it is a drive by wire acceleration system, check to see if you have brake lights.

Oh no!!! I would be pushing it out on to the street, ringing the RAA and blaming the missus (in that order). LOL

Did you pull any of the dash out? It sounds like a plug has been knocked off or something. Did you pull the plug on the ignition switch? Maybe that sent some signal to the ECU as a security issue. Might pay to ring an auto sparky or Nissan dealer (good luck with that one). Good advice above though - always have a wiring diagram on hand. Good luck with it, I imagine its a real PITA.