Please help me make D3 work?

[EcoCivic]

Ok so it's a bot of a long story, but I have an ECU and wiring harness from a JDM Honda Stream 1.7 in my 2005 Civic. It works very well, except that D3 doesn't work. I have tried almost everything I can think of to make D3 work, but no luck yet.

Basically the problem is that my car uses the range sensor to signal the ECU to lock out 4th gear, but the Honda Stream uses a switch in the shifter assembly to tell the ECU when it is in D3. The shifter on the Honda Stream 1.7 gets pushed to the side to engage D3, and it pushes a switch.

So I tried to find which pin on the ECU tells it when it's in D3. What I did first is I used a test light to ground each pin on the ECU's connector that goes to the car's harness while the key is on and the trans was in D, watching for the D3 light to come on. No luck. Then I tried using the test light to provide power to each of the pins, still no luck.

But then I realized that the ECU might not trigger the D3 light to come on even if I did find the pin. So what I did is lift the front of the car off the ground, start the engine, shift to D, and see if I could get it to downshift to 3rd gear by shorting a pin to ground or applying power. Still nothing.

So I am wondering if maybe something else is going on. Like maybe the MICU or the gauge cluster tells the ECU when the shifter is in D3. Is that possible, or would the switch directly tell the ECU? Or is there something I am overlooking? Thank you very much in advance, I would really like to get D3 to work.