IHMO one of the worst looking things in a engine compartment is the ratty-looking old wiring. I use Oil-Eater as part of my process to refurbish the wiring looms. Unlike other chemical cleaners that will remove the color off of wires, Oil-Eater does a great job without damage.
You will need a couple clean rags, scissors, Oil-Eater, ArmorAll and some cloth looming tape. (Looming tape is synonymous with 'hockey tape' which in case you're interested, is available in every color of the rainbow.)
Here's my process:
I work in small sections. If necessary to gain access, I disconnect one end of the loom. (Disconnect battery if necessary!) Don't disconnect more than you can remember. Mark everything and/or take lots of pics.
I start by removing the old cloth tape. This usually takes very little effort. Once the tape is removed I clean the wires with a cloth dampened with Oil-Eater. Once clean, I wipe them off with a cloth dampened with HOT clean water. I then wipe the wires with a cloth dampened with ArmorAll. I do this because OIL-Eater removes EVERY bit of oil/protectant from the wires and I do not want them to age prematurely or get brittle. I also clean the connectors with ArmorAll externally because they are typically already very brittle. If there are metal contact I can get to with a small stainless or brass brush, I clean them at this point too.
Now I apply the cloth looming tape, aka hockey tape, to replace what you removed in the first step. Cloth tape is not like electrical tape. It does not stretch and you do not need to overlap it by more than 1/4 of it's width. Take your time. You'll get the hang of it quickly.
Complete be reconnecting anything you disconnected and move on to the next section.
When you are done the harness will look as good as new. But it's not all about looks either... You may find during this process that grease/dirt or other foreign objects have gotten into the loom. With enough time and movement this stuff will wear through the wire's insulation. Examine all the wires as you clean them for damage and make repairs as necessary. Don't be tempted to make repairs with solderless connectors. Get out the soldering iron and heat-shrink and fix it right!
Edited by jdeitch, 07 August 2013 - 04:35 PM.