I have a 1986 pontiac firebird trans am with a 700r4 transmission, I don't know for sure if it's stock or not, but the vss is electronic, and the speedometer is electronic. It didn't have the plug for it so I went and bought one but under the car there's only a yelllow wire that sticks out of where the previous owners had cut it. The plug has a yellow and a purple wire so I'm missing one. What I need to know is where the purple/yellow wires come from so I can run my own. Problem is I don't have a clue where that might be. A possibly bigger problem is one of the previous owners ripped out all the cruise control systems, so I don't even know where to start. I didn't know if I was able to just wire it straight from the vss to the speedometer in the cabin either. Any tips?

 

I probably do not remember correctly...
I believed that a 1986 Trans-Am would have used the older style of VSS that used Brown and Black Wiring.
If your 1986 Trans-Am does indeed have a Factory/ OEM VSS as you described...

The Purple and Yellow pair of Wires can externally (outside of the Vehicle) be traced, by starting at the C100 Bulk-Head Electrical Connector.
This is the very large Electrical Connector on the Driver's-Side of the Fire-Wall in the Engine Compartment.
The Two Wires will pass down the Fire-Wall, and into the Transmission-Tunnel...
Remaining along the Driver's-Side of the Transmission to the Tail-Housing.

 

Look under the passenger side of the dash for a plastic yellow box. About 4" square and flat. If there is one that is where the yellow and purple wires from the VSS go to. That box buffers the VSS and sends digital VSS streams out to the ECM, speedometer, and cruise control.

RBob.