New Harness Sources ?

There's probably several situations that would warrant a complete harness replacement- the two most common that I can think of are a vintage car that has been damaged by time or mis-treatment and complete builds (resto-mods, race cars, custom cars) that require a lot of new circuits that never existed. Let's do vintage restorations first.

If you're restoring a very limited production car, your options may be few, and as always, it pays to find enthusiast groups that cater to your particular vehicle. There's bound to be someone who has been through the same situation and is willing to share their "secret" source. There's two vendors I've had experience with that can provide quality products for many older vehicles-  M&H Electric Fabricators, Inc. in California does a great job and provides good tech support during the installation. There's also a company on the East Coast-  Rhode Island Wiring Service Inc. that does excellent factory fit and finish harness'. They are also great on the phone, I called in with an odd question on a 1944 Dodge sedan, and the nice young lady on the phone called me right back with some helpful suggestions. So, as always, plan ahead on any wiring needs, do some research and if it's all too much- contact a professional !

On to the new builds- with race cars, you'll be doing most of the leg work yourself.. There's probably not a single off-the-shelf solution for every situation. But, you've got to start somewhere. Map out the requirements for your project,  Painless Performance does a nice basic kit that includes a lot of the parts needed. Of course you'll be adding your own circuits for engine management, transmission controls, communication and maybe telematics. Be sure that you're familiar with the regulations for your particular series- there are Guys who specialize in every kind of racing and should be able to give a heads-up before you show up for tech inspection and have issues. You should also be able to get good advice from your chassis builder and the supplier of you drive train parts as well. Plan the whole thing out, and don't loom up any major harness' before you're ready to test each system thoroughly. Bring in a specialist if this is not something that you feel comfortable dealing with.

With street rods and resto mods, you'll probably be adding modern features to an older or scratch built vehicle. The Guys at American Auto Wire have obviously been thinking about this- they make an excellent series of harness' with expansion and customization in mind. As always, plan ahead and get a little extra capacity (number of circuits)  so that you can add a few goodies along the way. Be sure to plan out any wiring that needs to go to mechanical items, and talk to your interior trim Guy before you start running any large harness'. If there's gong to be a stereo or navigation system, you may want to speak with a specialist in that field along with your trimmer- everyone needs to agree where stuff can fit and work properly before the wiring gets laid in! Advanced planning here will save time, money and aggravation later on.