@BoultsG I'll take a photo. My thoughts are to undo the harness wrapping for a length to reach the actual wires. For initial testing I've got some 100% brass dressmakers pins. I'm thinking to bend the wire a little so I can push in the pin lengthways through the pvc insulation and into the conductor strands. Then solder my extension wire to a pinhead. This way I won't be either cutting through a wire or major stripping.
Adding the resistor for trial purposes in the van cab should be a comfortable job whilst watching the laptop screen
MES EGR opening values.
Then we can try different resistor values.
.
In the event that my idea works then we work out how to install permanently, tidily and reliable.