I Like the Painless kits the best. If you are planning to totally change out your harness then I suggest Painless kits: 20102, 20103, or 20104. All three kits are the bulkhead pass through harness like in our cars so a direct swap as far as fusebox location and engine bay harness location.
20103: 21 circuits would be if you have a stripped down or race only car... No power accessories mech fuel pump
20102: 25 circuits has power windows, locks, fuel pump
20104: 28 circuit has everything 20102 has plus an extra accessory circuit, cruise control, power antenna.
This is a major task and it is easiest if the car is taken apart. I had my interior out including dash so I was not upside down as a contortionist running wires. This for most people is not a weekend job, plan a for the down time if this is a DD vehicle. I removed everything from the car and labeled sections and connectors on the original harness so I knew what was what and went where.
Next lay out the new harness on a table and look at every wire (they are labeled on the wire every foot) and seperate and group the wire by section in your car. They already come with the mfr idea of groupings, but I had a few that I put different places, so it was helpful to organize beforehand. Once I had them grouped I zip tied each sections bundle every 6" so that the wires would stay together and route easier.
Then I mounted the fuse panel in the factory location and ran each section to the area of the car to verify it would work how I wanted, and then did some more wire sorting of where certain wires would leave the bundle. This is also where you plan and add any extra circiuts(ie stereo systems, lighting, air ride, etc) so that they are all neatly run together and will look more professional.
Once I had that done and was happy with the layout I did another step which is not required, I then put each bundle in the braided wire wrap. I like it because it looks really nice and give the wires abrasion resistance and some heat resistance. That process is time consuming in itself, but worth it for me.
Once all the wires are run and routed to correct locations it is time for the real fun to begin... From that point it is the tedious task of putting all the connectors on. I professionally crimped (correct tools, which is another cost if you don't have them already),soldered, and heat shrinked every connection, Some will say solder is not required because the factory never did and if it is a good crimp it is fine. Well my experience is that most people including myself don't get every crimp right. By soldering I know every connection is good and solid. One bad failed crimp will at the least create gremlins in your systems and at worst create a Car- b - Que. Wiring is not an area where the phase "Good enough" has any business. Sorry , off my soapbox...
I changed all joint connections to GM weatherpak connectors because I like them best. I put all the connectors on in a section and then I would test it to verify it worked. Then move on to the next and so forth until done. Take your time, plan your layout. You will either need to reuse the factory connectors from your old harness and splice or buy new ends. I did all new ends. The engine side of the bulkhead harness is done the same way.
Only thing I wish is that I had known all the stuff I was going to add. I have had to sit upside down under my dash adding a few sub groups for additions I have made over time.
