323i into an M40 car - not cranking?

[bmwbreaker]

Hey guys

Got hold of a c Reg 323i that was well beyond economical repair but was running A1. I had a mint 318i lux on a H Reg and decided to convert the 318i with the 323i lump. Both cars are automatic as well.

I have converted to the newer round harness plug and virtually all of the key wiring colours were identical to one another (I did use a suitable pin out guide to ensure the right wires went to the right place). Put the ECU from the 323i in and found the 3 pin smaller plug that would not match the original plug on the car. Read somewhere that the green wire coming out of it needed to be put onto a live at the ignition (which I have done) I now get the fuel pump priming on ignition.

My issue is that I cannot get the starter to engage?

I have joined the two wires at the selector switch in case it was a problem there.
I have also run a jump lead from the earth point on the sump onto another earth in case it was an earth problem.
I’ve gone through the fuses and changed all of the relays.

On the gearbox the 318 had a 2 pin round plug going into the lower right side? What does this do? It’s not for the reverse as the lights come on? I tried bridging it with wire but still no start?

Anything else to check that I could be missing?

[Brianmoooore]

Starter motor signal wire is black/yellow. It gets its power from the green on the ignition switch, which is not dependant on the engine loom or any relays or fuses. Starter wire from the ignition switch is plain black, but changes to black/yellow at a plug and socket clipped half way down the steering column. On auto cars there is a starter inhibit relay connected into the black/yellow with plain black wires, located behind the glove box area.
The black/yellow then goes up and through its final joint, the engine loom plug and socket, and then to the starter motor solenoid.
Are you sure you have connected to the correct terminal on the solenoid? Have you connected the thick wire from the battery to the solenoid?
If all is OK here, check along the route of the black/yellow with a 12 volt lamp to earth and see where it lights, or not.

[bmwbreaker]

Starter motor signal wire is black/yellow. It gets its power from the green on the ignition switch, which is not dependant on the engine loom or any relays or fuses. Starter wire from the ignition switch is plain black, but changes to black/yellow at a plug and socket clipped half way down the steering column. On auto cars there is a starter inhibit relay connected into the black/yellow with plain black wires, located behind the glove box area.
The black/yellow then goes up and through its final joint, the engine loom plug and socket, and then to the starter motor solenoid.
Are you sure you have connected to the correct terminal on the solenoid? Have you connected the thick wire from the battery to the solenoid?
If all is OK here, check along the route of the black/yellow with a 12 volt lamp to earth and see where it lights, or not.

Thanks for the very in-depth reply. Found at the ignition switch a wire had been intercepted (black and yellow) and had originally been wired directly to the starter from this point! I intercepted the black and yellow wire at the c101 plug instead and the car is now running!