I am in need of a wiring diagram, or pinout of the ECM for a 2003 2.7 v6 out of a XL7 automatic. I particularly need the wiring lead that goes over to the dash & ? I have a full wiring harness for the engine, which covers most of the wiring, but need to convert the last section.
Do you have a pigtail for that 4th plug? If so, I can help you by telling you about wire colors and where they go.
-Eric
Do I have to change out the fuel pump and gauge for one with pressure and temp sensors? Or will it work without the sensors?

First, let me say again there are many ways and philosophies on how to integrate a engine swap's harness into a vehicle. I use all of the guage and hi power wiring from the original vehicle and 'splice' in the control wires from the new harness. So, what this means for the fuel pump and guage. I would leave the guage wiring undisturbed, it works fine as is. For the fuel pump, I use the original (car) relay and find the control wire coming from the ECM and splice that into the coil of the relay (low power side). On the xl7 ECM it should be the E61-23 and will be White with a Green stripe. To test put a continuity light on pointer on a know 12v source and then clip the ground clamp to this output from the ECM. Apply power and you should get 3 to 5 seconds of light and then it'll shut off. If correct, connect this to the grounding side of the fuel pump relay coil.
There, fuel circuit done!
Main relay is done in a similar fashion. The control wire is E61-9 and is Blue.
E61 refers to the 4th "magic" connector that interfaces the ECM to the real world.
-OR-
One can brute force it by using the vehicle's relays as discussed before and just ground the low side of both control coils. What happens then is that when the key is turned on the 12v gets applied to the high side of the coil and turns both relays on. This isn't an elegant solution but really insn't a problem. The fuel pump will run anytime the key is in the run position and the main relay will be on too. This is real close in operation to ECM control excluding low oil pressure and brain failure. So, that's another method.
Good Luck, -Eric