The 0-180 speedo are JDM only so glimited and turbo cars
(uk were 0-160mph), so thats a JDM speedo your working with.That grey wire on your speedo chip is not used on MR2 install, as Bob said the speedo signal comes from the gearbox sender to the ECU then the output speed is fed back through the loom to the engine ecu.
If that speed chip has gone faulty then no signal is getting back to the ecu hence you getting a speedo signal ecu fault code generated.
That type of chip work by slowing the pulse signal down by a factor of 1.62 thus after install your JDM KMPH clocks magically read MPH, this also effectively delimits the car because the speedo output signal is now slower
- so the Jap 180 kilometer per hour speed limiter is still on the engine ECU but you'd need to hit 180MPH to activate it, your not going to have a 180mph SW20 running factory EMS 
I'd remove that chip
(remembering to connect the purle loom wire back up) then test the car, if it starts working they you'll need a new chip (we have them instock) If its still not working then inspect speedo drive and start checking wiring with meter. (We have good tested e153 speedo drives instock should you need one)Good luck.
