So this is an E60XL
no serial number?
ok this truck is pre SEM (SX) controller , probably has the good ole EV100LX system in it.
You can find wiring diagrams on the controller unit on fsip.
But before you dive into that what kind of display does this unit have? Is it just a round guage on the dash? or is it premium display?
Either way when you press the accelerator pedal while on the seat with it in a selected direction it should display some sort of code on the display. The premium display will show the error code and probably have a pict-o-gram icon showing the drive motor. If it is just a BDI guage , those are usually still a multifunction guage and will show the error code while trying to activate the drive.

If the dataplate is missing look on the side of the frame along the battery and see if it is stamped there. Also look around the front cowl and around the fender area. It is usually in one of those places. It will be something like C108VxxxxxA (this is just an example)