That’s a great bit of info thank you, I will try that test and see what it does.If the FP relay is connected properly, there is no danger of "back feed" into the ECM....
That was my thought, when I cut that wire it came up with c41 and no fuel pump noise. I guess I’m best off cutting the wire that goes to the ecm then? So it doesn’t back feed?
While I have not opened an ECM to determine the root cause failure. My guess, based on similar circuits, is that the output drive transistor for the fuel control line has failed in the ECM. if so, having an external voltage connected to the Yell/Blu wire (somehow) will not damage the circuit any further.
Still, you may want to confirm that the Yell/Blu wire has continuity back to the ECM. If it is open, that could be the problem.
There is another potential problem that would cause the OEM circuit to fail. To test it, verify that the Org/Blu wire has 12V all the time - even with a load on it. If not, it may have a poor connection at the large white gang connector, or an open fuel fuse. It can be loaded by connecting jumper from the Org/Blu wire to the Yell/Red wire (disconnect the existing jumper before doing this test). This will cause the fuel pump to run, and the voltage on the Org/Blu wire should remain high (at least 11V) while the pump is running.