WRx fuel pump driver circuit

[BaldTurboFreak]

I have located the two pins that go back to the fuel pump driver out back. One seems to light up 12v briefly at key on and the other I assume is being PWM'd as it seems to have only a few volts with a quick spot check on the dmm.
Anyone know how the PNP ecu accomplishes this? Is there a specific 12v hot/pwm grounded circuit that uses the factory fuel pump driver?
The car is a 2002 bugeye wrx with an EZ30D/SEx-257/6speed. The stock ecu is still in the car for obd2 purposes, but currently without rpm signal from a 4cyl I only get a brief view of the factory behavior.

[Matt Cramer]

There is an enable signal that puts out 12 volts at all times the fuel pump is on, controlled by the standard fuel pump output. Then there is a 5V PWM signal that is triggered by an AND logic between the fuel pump output and PWM3 to control the fuel pump speed.

[BaldTurboFreak]

Thanks Matt,
Is the "and" function done within programming or is it run thru a logic gate?

[BaldTurboFreak]

Just thinking out loud here, but could I use the std fuel pump output to throw 12v at the one leg via relay or transistor, and say Spark H to PWM 5v to the other leg? Seems like a win/win in simplicity

[BaldTurboFreak]

Success! So I just mapped Spark H to the 5V TTl line ( Violet with white stripe, pin 15 on connector B136) and it works without sending 12v to the other line.

Now I just need to work on exporting a 4cyl 36-2-2-2 signal to the stock ecu from the megasquirt and I'll have the groundwork for a PNP harness to allow the masses to swap the 6cyl into a WRX and keep emissions devices intact

[Matt Cramer]

Thanks Matt,
Is the "and" function done within programming or is it run thru a logic gate?

Logic gate.