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The Top 10 Classic Electrical Snafus

The How-To Avoid Electrical Mal-

Photography by Mark Hamilton,

8. Underdash PowerHow many wires do you have jammed into that overloaded fuse box under the dash of your street machine? Most musclecar electrical systems were never intended to handle great electrical loads. So when you start jamming more wires into those "switched" and "unswitched" fuse-box positions, this greater load could eventually cause problems. Not only that, but it just looks cluttered.

The solution is to use a couple of MAD's terminal blocks, one for constant battery power and the other for "switched" power when the ignition key is on. The key is to mount two terminal blocks on a common aluminum mount located under the dash near the stock fuse block. The battery live terminal can pull power directly from the junction block off the battery under the hood. The second terminal can be switched using a relay triggered by a "switched" terminal on the fuse block.The battery live terminal should be protected with a fusible link located under the hood. Now you can bundle all those cockpit accessories to source power from these two terminal blocks and not overload the stock fuse block. If you really want to be safe, design a clear plastic cover for the terminal blocks so there's no way to accidentally short the block to ground.

9. One-Wire AlternatorsThere's confusion about aftermarket one-wire alternators versus typical three-wire alternators. A typical production-style three-wire alternator uses a voltage sensing wire connected to a main power distribution point in the wiring harness. This "sensing wire" allows the voltage regulator within the alternator to read electrical system voltage resulting in proper voltage delivery to the wire harness. A three-wire alternator also has a special switched "turn-on" wire, and this wire can also be used to operate a warning light at the dash. A one-wire alternator requires internal voltage created by the spinning alternator to trigger or start the charging process since it does not have a voltage-sensing trigger connection. When the engine is started, a one-wire alternator must achieve a certain speed in order to reach that internal voltage. Once that occurs, the one-wire alternator will begin charging and will charge even at very low engine speeds. This means you must simply rev the engine above a given rpm (usually around 1,500 depending upon the pulley ratio) before the alternator will begin to charge.

According to a rather substantial treatise on one-wire vs. three-wire alternators on MAD's Web site, the voltage drop from the alternator to the battery with a long wire can compromise the performance of the one-wire alternator compared to a three-wire. This is why MAD recommends using the GM 10Si or Cs130 alternators, even in many Ford applications. This is not a condemnation of the one-wire alternator. But if you want the most from an alternator, the three-wire version is slightly more efficient.

10. Fusible LinksWhat the hell is a fusible link? Think of it as a safety net for your electrical system. Most domestic cars from the mid '60s through the '70s source all the electrical power for the car (except for the starter) from either the main charging harness or, in the case of GM cars, from the smaller wire pulled directly off the positive battery terminal. To protect the wiring harness, most of the car companies used an inexpensive wire called a fusible link that is designed to melt when the current demand exceeds a given level, like from a direct short. This protects the wiring harness from damage, but also immediately disables the car. Often, ignorant wire hackers set the car up for a potential wiring meltdown and subsequent fire by eliminating this fusible link.

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