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8 Things Every Wiring Harness Buyer Should Know
Home / 8 Things Every Wiring Harness Buyer Should Know

Not all wiring harnesses are created equal. There are big differences between wiring harness brands. Since most people don’t know what these differences are, most wiring harness manufacturers take shortcuts.

If you’re buying an automotive wiring harness, here are eight things you should know BEFORE you buy:

#1 – Are the connections soldered?

There are two ways wiring harness manufacturers connect wires to the fuse block and switches: crimping and soldering. The crimp method is nearly always incomplete, as it’s tough to grab every strand of the wire. Additionally, crimped connections overheat much easier and can literally “shake loose” in the right circumstances. Soldered connections, on the other hand, don’t have these problems. Soldering is essential to wiring harness durability and is the absolute best connection method.

#2 – Is the harness compatible with a modern alternator?

Most universal wiring harnesses are rated for a 60-75 amp alternator. This is a problem, as modern alternators (even those produced for older applications) are usually rated at 100amps. A harness that’s designed for a 60 or 75 amp alternator will overheat and potentially failĀ fire when connected to an alternator rated at 100amps.

#3 – Is the harness compatible with modern halogen headlights?

Many universal harnesses are designed to accommodate standard sealed beam incandescent lights, yet most older vehicles have halogen sealed beam replacements. The wattage difference between halogens and incandescents is substantial (often twice as much). If the harness uses 18 or 20 gauge wire, the wiring will overheat and the headlights will be dim. 14 gauge wire for the headlights is best.

#4 – Is the harness expandable?

Many wiring harness are made only to accommodate the number of circuits listed. This means, to add a circuit, you need to replace the fuse block, upgrade the wiring, and possibly even buy a whole new wiring harness because expanding the circuit might just be too much of a pain. Look for a wiring harness that can handle the expanded current draw if you decide down the road to add a circuit or two.

#5 – Is the harness made from real copper wiring?

A lot of wiring harness companies will use a copper alloy – a copper “blend” – for their wires, as opposed to 100% OEM-quality copper wire. While copper alloy wires are cheaper, they can lead to voltage drops across the electrical system of your vehicle. NOTE: It’s just as important for the terminals to also be made from copper (or brass), as these are higher quality than off-shore knock off terminals made from copper alloys, aluminum, or even tin.

#6 – How much wire do I get?

One of the easiest ways to save money on a wiring harness is to reduce the amount of wire you use. It’s a lot easier to cut wire than it is to add it, so look for a wiring harness that includes enough wire length for your project. Hot Rod Wires, for example, provides

  • 20 feet of wire for circuits going to the rear
  • 15 feet of wire for circuits going to the front
  • 8 feet of wire for circuits in the engine compartment

That’s what we feel is enough wire to do the job for any project. Most other companies use less (some far less).

#7 – Are hot starts a problem?

“Hot start” refers to a problem that plagues vehicle owners in hot climates. Basically, if the wire that energizes your starter is just barely big enough to carry the current your starter requires, and the wire gets hot (over 120 degrees or so), the starter can’t draw enough current and the vehicle won’t turn over. We call this a “hot start” problem. The solution is easy – use heavy 12 gauge wiring to energize the starter. Many wiring harness providers don’t do this, using 16 gauge wiring instead.

#8 – Who provides technical support? Do you provide installation advice to your customers?

Wiring can be frustrating. It’s helpful to have someone to talk to about installation problems and questions. At Hot Rod Wires, we provide technical support (including help with difficult installation problems) to our customers 7 days a week. Our technical support is backed by 50 years of automotive electrical experience.

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