Diodes, Resistors & Transistors

Controlling the Electron Flow

Your vehicle's electronics are the unsung heroes of modern motoring. They light your speedometer, recharge your battery, tune your radio stations and keep your engine running. And NAPA is here to help keep those electrical systems in top shape with the quality parts you expect.

While electricity needs a completed circuit to work, in some cases that circuit needs to only flow one way. That's where the humble diode comes into play. A diode acts like a check valve or one-way bearing, only allowing electrons to flow in one direction. There are all kinds of diodes inside the computers and modules found on modern vehicles.

Inside an alternator, a special array of diodes (called a bridge rectifier) converts alternating current (AC) to the direct current (DC), which powers your vehicle. Sometimes your alternator needs a special heat sink just to keep the temperatures at bay. So if your Nissan Altima's alternator is acting up, sometimes it just needs a replacement alternator diode.

Resistance Is a Good Thing

In "Star Trek," the Borg said, "resistance is futile." However, in your vehicle, resistance makes components work. The heater blower motor in your GMC Yukon would simply run wide open at a single speed if it wasn't for the blower motor resistor. A resistor limits the current in an electrical circuit. By using different types of resistors, you achieve various blower motor fan speeds. For older cars, there is even an ignition coil resistor (sometimes called a ballast resistor) to limit the current that reaches the ignition coil, which makes your coil last longer.

If you swap out an incandescent bulb on your Ford Focus with an LED, you might need a lighting resistor to make things work properly. For example, some LED turn signal bulbs don't draw enough power to make a turn signal relay work properly, leading to a fast-flashing light instead of the slow clicking everyone expects. A loose light connector on your Toyota Camry can lead to flickering headlights, while a broken resistor connector could keep your engine from running at all. Most people don't inspect their electrical connectors during routine maintenance, but when things go wrong, it never hurts to give them a look. Electrical connectors can actually melt in some cases, leaving the metal connectors inside unable to touch. Electrical connectors should remain firmly in contact with each other and clean from corrosion.

Replacing Diodes & Resistors

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