I ride a Magic Pie V5 and can totally understand your desire to keep this fine motor going.
Overview: As your changing the location of the internal controller to outside the motor housing. The motor's wiring which includes the 3 larger phase wires, as well as the 5 smaller hall sensors wires. Must be extended to where the new controller will reside.
The existing 8 pin wiring harness with the wiring to the peripherals will then go directly to the new controller location, as well as the battery wiring.
Internal Magic Pie 3 controller...
Phases: Large YELLOW, GREEN, and BLUE single connections. Halls wires go to BLACK 6-pin connector.
At the controller to phase connections, I would recommend bullet connectors to aid in changing the phase to hall configuration if needed. Or at least be prepared to swap leads before final connections made.
May be a great time to add a temperature sensor to the motor. Especially if you plan on pushing it harder than normal.
If I were to do it, I would procure a 9-pin motor connector and harness length that would reach my new controller.
This would have the extra-large needed phase wire in it. And allow easy removal of the motor and wheel with a HIGO connection.
Considerations would be that the phase wires be of sufficient size to carry your maximum current. And that the cable outside diameter would fit thru the axle opening.
An example...
As seen here...
Just an example.
See this link for example pictures of the motor's wiring connections and information. (Other links are in this thread...)
Magic Pie 3 controller - end of the game? How to salvage great MP3?
As far as the upper harness connections to the controller go, I do not know of any verified wiring color aids such as the one below for the M.P. V5... although the second MP3 harness picture shown below has some.
In your case you will have to
carefully identify or verify what color of wire goes to each pin at the 8-pin motor harness connection.
And label them accordingly to which pin they go to at the top pin connectors. I.G. Throttle, Brake, Grounds ECT.
Now there seems to be 2 types of MP3 harnesses that I've seen... hopefully one matches yours.
And this one...
This careful identification and verification of wiring colors may be helpful to others in the future... (hint, hint)
Then just match up your controller's wiring to what to hook up too.
Please note that your controller requires a "key lock" connection to power it up.
Something extra not found on the original Pie.
Regards,
T.C.