[Richard L]

Just to confirm, you have connected the white wire to the ECU side and brown to the wastegate solenoid (BCV) side after cutting the ECU cable.

Please disconnect the white and brown wire and check the continuity of the brown and white wire under the following conditions:

1. no power to the system (gauge on or off) ......... open circuit
2. ignition on, gauge off ......... open circuit
3. ignition on, gauge on ...... closed circuit