Ok thanks for that. I think what has thrown me here a bit is that my harness is slightly different for some reason. Yours looks like it's hooked up exactly like the wiring diagram I posted somewhere up there ^^^^^^ but on mine it has the same four wires terminating at the plug but in addition it has another short spur coming off with black and red/grey wires terminating at another plug, on the other side of this additional plug was the LED connected directly into the opposing side. I have now cut the LED away from the terminals and soldered a length of wire between them so I can have the LED up on the bars. The LED has a resistor in line under the heatshrink which I assume is correct.
So these appear to be duplicate wires. I've just removed the tape and can confirm these wires are joined to the others.
So am I right in thinking I don't need to do anything with the red/grey in the main plug do you think?