So I got the replacement harness from the dealers, came to around £30-35 including VAT. Thought I would give a short description of how to fit it seeing as I couldn't find any info on the forums. I didn't want to cut the existing wire inside the wheel arch as this would've made a weak point along the harness, which has a pretty thick shell due to the abuse it can take.
The harness attaches to the brake pad sensor and the ABS sensor on the arm, and goes through a little rubber grommet in the back of the wheel arch into the engine bay. By taking the airbox out, you can feel down behind the strut mount where this comes through, and feeds up into the wiring loom (which goes between the battery and the back of the dash). You can access this loom by unclipping the top of the plastic enclosure that it is housed within. There are a couple of looms, but you can feel that the harness goes into the thicker one.
What I was looking for was a decent access to the cable where I could cut it, bare the wires and solder the new harness in. The loom is this nasty black sticky tape, which I cut all the way along to where it separates to go down to the ABS/ECU unit. Now the black harness cable is made up of 4 wires, 2 of which go down to this unit and 2 which double back to go somewhere else. Once I knew I had the right cable from the loom (BE CAREFUL because there are 2 black wires of a similar thickness) I cut it at the point just after it comes through the wheel arch and pulled it through the loom so that I had lots to play with.
From here, you can disconnect the existing harness from the wheel arch, plug the new one in and feed this through the hole in the arch (fixing in the rubber grommet as you go). Feed the new wire up into the loom, bare the ends and solder them to the end of the existing harness (that you just cut).
Re-assemble and hopefully when you drive up the road your ABS light will go out and the car will stop beeping at you
Any questions just PM me.
Will
