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Wiring Harness Upgrades

There’s More To It Than Just Connectors

Jeff Smith Aug 1, 2001

Step By Step

This may look like a jumbled mess of wires, but if you pay attention to details, there are plenty of opportunities to improve your car’s performance and fun factor with a more efficient wiring harness.

M&H uses only factory-style connectors to duplicate the stock harness look—if that’s important to you.

The harnesses also include all factory-style plastic push-in hangers or clips used in the original harnesses.

This is a shot of a new M&H ignition harness that includes the resistor-wire connector and oil pressure sending unit connection.

One of the slickest items M&H offers is an alternator conversion for an existing harness that will convert the old external regulator alternator to a 10Si-style alternator.This is the alternator plug-in conversion

And this is the cool jumper connection that does not require cutting the wires on the existing harness.

If you order a custom harness for a 10Si-style alternator, for example, the harness will be built with the appropriate connectors already in place with no jumpers required.

High-output alternators require a large-diameter cable to reduce resistance. Original factory harnesses used a 10-gauge charge wire that is usually sufficient for most loads.

M&H can also supply a choke feed wire that is energized whenever the key is turned on. For our harness, M&H left this wire long so we could make our own connection for an electric choke.

If you know your street machine, you might feel like you’re actually wired right into its main engine harness. That would actually be very cool. But whether you’re hardwired or not, you’d want to make sure that all those electrons made it to their intended destinations as easily as possible. That’s what your wiring harness does for you. After 30-odd years of heat, vibration, abrasion, and abuse, the harness that connects your car to your engine might be in need of salvation.

The obvious answer is to bolt in a new wiring harness and be done with it. If you are knee-deep in a ’60s or ’70s musclecar restoration, that’s the hot ticket. But most Chevy High Performance readers are more interested in modifications rather than pure restoration. With a minimum of effort, you can order just about any kind of modification into your wiring harness that you’d like. This means a small increase in cost over a stock harness, but it’s worth the investment.

We focused our attention on the engine harness since that’s where we centered a majority of our modification ideas. We contacted M&H Wire Fabricators to get connected into the details of wiring harnesses. M&H has been making replacement wiring harnesses for musclecars and classic vehicles for years using exact replicas of the original connectors to give restorations that factory-fresh look. These same harnesses can be used for hot rods as well.

For example, M&H constructed a harness for our ’67 RS street-driven small-block Camaro. We planned on several engine compartment changes including the addition of an aftermarket ignition system that would require 12-14 volts to the ignition coil. M&H also offers a one-wire electronic-ignition conversion that, when the distributor cap is in place, looks just like a points distributor.

A very popular modification to many early Chevy musclecars is a charging system upgrade. The older, external regulator alternators are on the weak side compared to today’s 90-amps-at-idle wonders. M&H offers both add-on connectors that will convert your existing harness, and a new engine harness that will incorporate these changes directly into the existing harness. M&H can supply connectors even for the most recent CS-130 and large CS-144 alternators. These latest-generation alternators can crank out some serious amps to power even the most electrically challenged street machine.

Another electrical addition that might be useful includes connections for an electric fan and relay. Electric fans generally pull in the neighborhood of 15 to 30 amps, which requires a relay. This allows a light-duty switch to control the relay that actually connects power to the electric fan.

As you can see, there are many ways you can customize your street machine with electrical goodies that still allow it to look much the way it did when it rolled off the assembly line. Or you can electrify your ride with all kinds of outrageous electronic goodies that are state-of-the-art 21st-century cool. Either way, your own creativity is the only limit.


M&H Electric Fabricators

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