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Need Wiring Harness Tips & Tricks

Alot of good advice. I like using spreadsheets to plan out much of the wiring.
Having a list of the original circuit numbers, wire colors, wire gauge, and connecting terminals then matching that up to the new wiring harness wire colors and circuits.
If your doing some custom wiring, with non-stock type parts, then the planning stage is a good place to make sure the wire gauge and circuit fuse are sized correctly for the loads.
If planning future modifications, you can add the wires to the harness.
For example, in the rear body harness you might want to add a fused constant hot wire for an electric trunk release, or trunk light, or audio amplifier.
Also, an additional ground wire, and if planning EFI, fuel pump power wires. Lights, power, fuel pump wiring ran down drivers side like stock, audio signals, speaker wires and such ran down passenger side of car.
Not that common on cars, but if you plan on using the vehicle to tow with, then the trailer wirings (lights, brake controller, power, ect.)

Many kits just have the fuse block and long wires, with no connectors to separate the harness sections, or bulkhead connectors.
I like re-using the factory bulkhead connector shells if in good condition, but that requires buying all new packard 56 terminal connectors.
I do remove the heavy current loads from the connector by bypassing the firewall block for the alternator, and using relays in the engine compartment for headlights, a/c compressor, electric fan(s), and horn.
I don't care for the pre-wired headlight connectors with the pigtails that are to be spliced to the actual harness.
I just buy the Packard 59 (larger than the 56 series) headlight terminals, but I also spent the $100 for the packard 59 crimpers. If not using the correct crimpers, or splicing the pigtails, then I would solder the connections, and heat shrink the splices using adhesive heat shrink (like 3M 3:1.) Plan your splices also. Staggering the wire lengths of where the splices occur can reduce the bulk look of the harness, but if the wires need a tight bend, then you might be better off with the bulk look in the harness so the wire can bend after the splices.
I try not to have wire splices or taps, with wires just going from crimped terminal to crimped terminal. If needing an additional wire in the circuit, like connecting a daisy chain of terminals, I like keeping the wire in one piece by striping the wire at the correct length for the first terminal, fold the wire over onto itself and then crimp the wire.
Twisting the harness. If you put a light twist into the harness wire runs, like the factory wiring, it allows the wires to go around bends easier.
When covering the harness, leave room between the terminal connector and where the harness wrap starts to have room to switch the terminal connectors in the shell just in case they were installed into the wrong shell cavity.
Depending on the look your after, consider using braided wire loom. The regular general purpose stuff is inexpensive, likely cheaper than electrical tape, and allows the wires to flex easier. For under the dash, the flex braid that uses velcro to wrap around the harness makes wraping (and unwraping) the harness easier than trying to remove electrical tape. There is also high temp braided wire looming products for around the exhaust / headers, but it can get evpensive.
 
My number one tip: go to eBay and buy a laminated full color wiring diagram for your exact car for $15 approximately. Should be a copy of the factor service manual, just rendered in color, and you have to account for the options of floor console, 4 speed, auto on the column, back up lights, AC/heat, type of engine (hemi vs. others) all this will be a little different so look at the diagrams in the factory service manual and buy a diagram on ebay that closely approximates the options on your car! Makes things WAY easier.

Second thing: consider testing components with a 12v "wall wart" adapter with alligator clips on the ends (you basically sacrifice one adapter you have in the basement; I have 50 of them from music gear). I have not done this second tip yet, but will in the future to save myself the headache and test the end electrical item first and work backwards to the fuse box.
 
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