When something goes wrong in wiring or an accessory, the flow of electrical current can create heat that damages wiring and accessories or even starts a fire. Fuses contain a soft conductor that melts easily. When a short circuit or overload happens, the fuse will quickly melt and break the circuit, killing power to it before there is too much heat.
You can tell a fuse is blown by looking through the clear plastic. You’ll see solid, bright metal when it’s OK and a separation in the metal when it’s blown. When a fuse blows, suspect electrical system trouble, but it’s worthwhile to try a replacement fuse first. If it blows again, diagnose the problem and repair.
3. Look up the amperage rating of the fuse. This will be listed inside the fuse box lid, outside the lid or in the owner’s manual. Get a fuse of the same amp rating. Using a fuse that’s even a few amps higher than the circuit’s capacity can cause serious trouble.
4. Turn off the ignition, or, if dealing with a circuit not controlled by the key, turn off all accessories on that circuit.
5. Pull the fuse straight out. If it doesn’t protrude far enough to grab it, gently pull it with a narrow pair of pliers.
6. Replace the new fuse by lining up its prongs with the holes in the box floor, then gently forcing it down into the box. For under-hood fuse boxes, inspect the seal inside the groove in the cover and replace it if it’s broken to prevent water and road salt from damaging electrical circuits.
7. Replace the cover by inserting the prongs through the hinges, rocking it closed and forcing it downward until the attaching clips or locking mechanism latch tightly.
• Narrow-jawed or needle-nose pliers
• New fuse
Affected trucks include model year 2008-2018 Freightliner Cascadia and Western Star 4700, 4900, 5700 and 6900 trucks. DTNA says after hard brake applications, the brake light pressure switch may not activate the brake lights with the light application of the brake pedal.