Power windows problem

Hi 
I have a 1986 clipper cabby with power windows. Somewhere along it's life someone has butchered the wires for the windows. 
The windows motors work ok had them hot wired up to test them. I have the right power form the fuse box and from the ignition but still not working. I have traced a .5mm or .75mm black wire that runs along side the red to the fuse box, it has been cut at the fuse box end! Does anyone know where this is supposed to go? It's the only wire that I've not been able to find a place for and think it may be the cause!!