* Short in the wiring harness: This is the most likely culprit. Worn insulation on the wires, especially near the taillights, can allow the wires to touch, creating a short. This is often exacerbated by corrosion or damage from water intrusion. Check the wiring carefully, especially where the wires enter the taillight assemblies. Look for frayed or melted wires.
* Faulty brake light switch: This switch is located near the brake pedal and activates the brake lights when you depress the pedal. A faulty switch can cause a short circuit, continuously sending power to the lights and blowing the fuse.
* Short to ground: A wire might be grounding out (touching metal) somewhere along the circuit. This could be anywhere from the brake pedal switch to the taillight bulbs themselves.
* Shorted brake light bulbs: While less common, a shorted bulb filament can draw excessive current and blow the fuse. Check all brake light bulbs (both sides) for any signs of damage or internal shorts. A bulb that's intermittently working is a strong indicator.
* Faulty Center High Mounted Stop Lamp (CHMSL): The third brake light (mounted on the rear deck) is also part of this circuit. A short in this light or its wiring can cause the same issue.
* Trailer wiring (if applicable): If you regularly tow a trailer, a short in the trailer wiring harness can backfeed into the vehicle's system and blow the fuse. Disconnect the trailer and see if the problem persists.
Troubleshooting Steps:
1. Check the bulbs: Replace all brake light bulbs (including the CHMSL) with known good ones. This is the easiest and cheapest step first.
2. Visual inspection: Carefully examine all the wiring related to the brake lights. Look for any signs of damage, chafing, corrosion, or water intrusion, especially near the taillights and the brake light switch.
3. Test the brake light switch: You might need a multimeter to test the switch's continuity. A malfunctioning switch will often show a constant connection even when the brake pedal is not depressed. This is best done with the help of a wiring diagram.
4. Trace the wiring harness: If you suspect a short in the wiring, carefully trace the wires from the brake light switch to the taillights, looking for any breaks in insulation or points of contact with metal.
5. Use a test light or multimeter: This allows you to pinpoint the location of the short circuit by systematically checking the voltage at different points in the brake light circuit. This requires some electrical knowledge.
Important: If you're not comfortable working with car electrical systems, it's best to take your Intrepid to a qualified mechanic. Improperly diagnosing and repairing electrical problems can lead to further damage. Remember to always disconnect the negative battery terminal before working on any electrical components.
