So I have the 85 Brat, in the instrument cluster on the back there is two plugs coming off the top. One is the VSS, yellow and black,

What is the other one? Light Blue and white wires?

I think they all have this white / blue or is it blue/ white trace?

With a clear soft insulated bullet terminal say 100 mm from the cluster? I dunno, once thought it was an earth or caused trouble when I left it disconnected

VSS , pull the other leg , or is yours turbo? No, not an 85 surely?

Check for factory service manuals online ? Wiring diagram might help. I recall some service manual which showed a breakdown of each plug with pins , it’s function , etc.