Fuse box diagrams 2003 peterbilt 387 - Cars & Trucks (2025)

FAQs

How do you diagnose a bad fuse box? ›

Your fuse box will have two sets of fuses. At the bottom will be 15-amp and 20-amp screw-in fuses with glass faces that are exposed and visible. These fuses will service branch light circuits and outlet circuits. At the top will be 30-amp or 40-amp cartridge main fuses for ovens, laundry rooms, or stoves.

There are two fuse boxes, one located near the engine or under the hood and the other is located near the driver seat.

The two most common symptoms are: An overloaded circuit which will blow the fuses in question. As a result, this will cause any associated devices to disconnect. Lastly, the smell of burning is another clear indication of a faulty fuse, as well as the smell you will notice burn marks on the fuse box.

Some of the symptoms of a bad ignition relay include an unresponsive ignition switch, stalling, and a drained battery. Your vehicle can also start intermittently. A brand-new ignition relay typically costs around $10 to $100.

A switched fuse is one that only has power when the ignition is turned on, while a constant fuse always has power.

The main relay acts like most other relays, but it specifically connects and controls the fuel system and the PCM. The relay turns on and activates both these systems when you turn your key in the ignition.

Understanding the Fuse Box Anatomy

If it's a breaker panel, you'll see columns of circuit breaker switches with levers marked ON/OFF. Whenever the breaker trips, it falls back to the 'OFF' side, so you'll simply flip it back to 'ON'. For a fuse panel, you'll basically have a column of fuses lying side by side.

The main fuse box is typically located under the hood, while secondary fuse panels might be inside the car, often near the dashboard or steering wheel. The fuse's wire conductor breaks when the current exceeds the ampere limit, which manufacturers usually define along with different color codes on each fuse.

This specification describes the requirements for a static transfer switch, (“STS”), and a cabinet-matching power distribution unit, (“MDU”) system. The STS/MDU system shall include an STS module connected to a load side PDU module that houses a stepdown isolation transformer and 208/120V load distribution.

Is there a fuse box under the dash? ›

Most vehicles have two fuse boxes, with one under the hood and the other in the cabin. You can usually find the other fuse box in the dashboard on the driver's side, but some manufacturers also place it below the glove box. If the interior fuse box isn't there, you can try checking the luggage compartment.

The vehicle's fuses are located in two fuse boxes. The interior fuse box is underneath the steering column. The under-hood fuse box is in the engine compartment next to the battery. If something electrical in your vehicle stops working, the first thing you should check for is a blown fuse.

The power distribution center, or fuse block, located under the hood houses most or all of the vehicle's fuses and relays. It contains a relay for the ECM that is powered up when the ignition key is turned to the on position.

The thin metal strip breaks apart when the fuse blows, terminating the electrical connection. Sometimes, the metal strip will also melt and discolor the glass window. If that happens, you might notice a burnt smell when you approach the fuse box, also known as an electrical panel.