700-R4 Speedo Wiring

I believe I have an 88 tranny. It has the speedo sensor rotor that has a purple wire and a yellow wire. Can anyone tell me what the function of each of these wires are? I am trying to wire a VDO speedo and have run up against a wall...

 

Assuming you have a fuel injected engine .
And, you have a VDO programmable speedo, The vdo signal should
feed off either wire.
Ppl. is VSS low,it varies from.60 to 12vdc as wheels turn.
Yell. is Vss High " " " "

Hope this helps.

 

If your speedo only has one wire to the sensor, you can hook either to it and just ground the other.