Electric or Mechanical?

on a chevy transmission, how can u figure out if it is electric or mechanical for a speedo? I have yet to order the auto-meter gage pack and i need to know wich one i need. I saw a plug for wires on drivers side.

well what kind of chevy tranny do you have ?

powerglide ? turbo 350 ? turbo 400 ? 200R ? 700R4 ? 4L60E ?

look on the left side, there should either be a place for a plug, or a hole to screw a cable onto.