maz duh
+1y
There are a couple of options for extending your harness. You can cut up your harness and splice in extra length from a donor harness or just get some bulk wire in the same gauge and solder it in to lengthen it. The donor harness method will make for less solder joints and it easier to do because you are matching like colours of wire this way which can be less confusing if you not a wiring guru. Be sure to solder your wires together and seal them back up with some nice heat shrink tube, the kind with the glue works really well. Another helpful hint is to stagger where you make your cuts in the harness to avoid a fat spot under the tape or loom. This also lessens the chance of having one connection short out on another down the road. As far as what to run it through the firewall with I have always reused the factory book or scoured the wrecking yard for a suitable doner. The one in the link you posted is really nice looking and would also do the job nicely. Hope this helps you out a bit anyways, good luck.