I just acquired a 90 mustang gt in a trade. Car is a auto and has supposibly a c6 trans swap in it. Heard this wasn't a good swap, but regardless went to change out heater core realized there was no speedo cable attached to speedo. From research I have done looks like there is no way I can just hookup a speedo cable is this correct? Car is on a megasquirt so was thinking of going there digital dash but if I can do it way cheaper would prefer.