Still got the old engine ?
Then trace back the wire from the solenoid to the engine plug.
If you are doing this stuff for a living get the appropriate tools so you can pull the terminals out of the plugs, crimp new terminals on the new engine wires and refit them into the old plugs.
Once you get the hang of it swapping terminals & crimping is about 3 times faster than cutting the wires and doing a proper solder & heat shrink splice.