OK, I have the car in front of me with the shell off.
Looking at mine and knowing how it works, your car is in the door open, signalman out position.(I had to adjust the gears in mine for a bindup problem)
The empty plug goes to the motor where the external wires were added.
White on the left of the plug to the right side of the motor.
Yellow on the rt side of the plug to the left side of the motor.
These wires are routed down into the undercarriage at the barrier to the interior on the back side as you have it pictured.
The signalman goes on the end of the lever slanted across the floor. he has 2 small black wires through the feet, down the bottom of the lever through the undercarriage to a plug on the back side of the circuit bd labeled out6V. since both wires are black polarity will have to be tested.
6V on a LED is not going to hurt it if you have it backwards, it just wont light up.
Give Midge a buzz and see if you can get the signalman with wires. If not we will have to get creative.