Ok i have a 91 formula 700r4, with a carbed sbc. my question is which wire from the tranny(color) is supposed to go for the speedo. i cut back most of the wire harness that i didn't need, but as of now i have a blue,yellow, purple and green wire hanging off the tranny. which do i hook back up to the speedo?

 

Purple and yellow. The purple is the ground. Yellow is considered the signal wire. But you CANNOT hook it up directly to the instrument cluster. THe signal needs to be converted (from 0-12V pulses to a gnd trigger) by either the ECM of the yellow buffer box that used to be on 'birds before 1990.

Hope this helps.
Lou