Speedo sender on 85 Prevost

[Merlin]

Where is it?  Looking in the rear panel there is a wire connected to the speedometer lug.  Same for the front panel.  That indicates to me the sender is located in the rear possibly on the tranny?  However a bus "expert" told me the sender is on the left front wheel and operates similar to a bicycle speed pickup (magnetic).

OK, that makes sense because another bus expert replaced all brake drums and the speedometer has not worked since.  Indicating to me that the mag pickup is either off kilter or left off altogether.

My next move is to run it up on front ramps then search around the left front brake drum.

Any guidance?  By the way, I do have all the maintenance manuals (huge books) and there is no help in there reference the speedo sensor.