Does anyone know what the pink wire is for on the fuel pump ecu harness? I have a tech checking the wiring, but he is unable to verify what this wire is for.

 

https://www.clublexus.com/forums/per...g-diagram.html
This might help. Don't know the year of your car though.

 

the pink wire is the "DI" pin, here is a description of its function

Engine ECU FPC & DI Pin Operation

The engine ECU outputs a 0V to 5V Pulse Width Modulated (PWM) signal on the FPC pin which is connected to the Fuel Pump Control ECU to control the speed of the fuel pump.

The Fuel Pump Control ECU also has an output to the engine ECU that indicates that the Fuel Pump Control ECU is healthy. The output from the Fuel Pump Control ECU connects to the engine ECU pin labelled DI. The Fuel Pump Control ECU connects the engine ECU DI pin to battery voltage when the Fuel Pump Control ECU is healthy.

It is worth noting that at least on some engine ECUs that if the engine ECU DI pin is not connected to battery voltage then the engine ECU will stop the PWM output on the engine ECU FPC pin which will then signal to the Fuel Pump Control ECU to turn the fuel pump off.