The electric motor needs to be connected to the wheels. In general terms, there are 2 requirments:

1. The traction power goes thru a differential. The reason for this is, when turning a corner, the inboard wheels rotate slower that the outboard wheels. Unless of course you are using hub motors.

2. The traction power goes thru a gearbox. Unless of course you are using hub motors.

Solution1:Typical of many conversions

Most conversions have an electric motor connected to the original gearbox, and thence to the differential. So the problem now, is connecting to the original transmission. The transmission will have a splined input shaft. So, now the problem is to connect the electric motor shaft to the splined shaft with a coupling. On one end, the coupling accepts the motor shaft with a key. On the other end of the coupling, is a female spline, that connects to the transmission. Where do you get a female spline. It is a challenge for most to machine a female spline. It is easier to mount the female spline that was on the original clutchplate. In the following image, the clutch plate (with spline) is bolted to a steel coupling.

The remaining mechanical challenge, is to bolt the motor to an interface plate, with bolts to connect the motor to the transmission.

The following images show an electric motor, with 2 more types of a clutch adaptor.

Solution 2: Common to the Solectria truck conversion.

In this solution, the transmission is replaced by a gear reduction, implemented by timing belts and gears. Very original. It is possible to do this with an AC motor conversion, because an AC motor has a broader speed range than a DC motor. No gear shifting is necessary. In addition, mounting the motors, as shown in the image, frees up space to mount the battery box.

Explanation: The first picture shows the truck beds tilted up. If you look closely, you can see the motors on the left, and the battery box, located in back of the cab. The second image shows dual AC motors bolted to a housing. And coming out of the housing is a short drive shaft.

The following image shows the interior of the housing - where the gear reduction takes place. The large pulley drives the dreveshaft. Solectria did a terrific job. Hats off to the engineering team!