W58
 

I have A 89 supra with the w58 and the front seal is leaking so I took it to a transmission shop and they said that the rubber seharbor rock hard and cut a grove in the shaft so they said they will try to sand it down some to help it seal and new front and rear seals for 150$ or replace the shaft which is 850$ so I found a w58 out of a 87 supra but mine has a little box with a wire coming out of the top of the tranny and a wire coming out the side which is the backup lights switch right and the 87 w58 doesn't have the top wire. So what is it for.

quite possibly its the abs sensor. as your have the 89 abs was standard from then on, for the 87-88 it was an option. a pic of would help

ABS was still only an option in '89... and later years in the US. And you're right. It'd be for the rear ABS speed sensor.