92-95 Civic CX upshift indicator troubleshooting
The Civic CX P05 ECU uses ECU pin D18 to send a ground signal to the upshift indicator bulb in your cluster.
Other models of civic and integra have an ECU circuit board that may use pin D18 for automatic transmission shift lock control. Even if your ECU is configured for a manual transmission, this circuit may still be present in your replacement ECU.
If your Civic CX is using a non-CX ECU and you are experiencing this problem, simply cut or disconnect the wire at your ECU pin D18.