Possible Causes:
* Short to Ground in the Taillight Circuit: This is the most likely culprit. A frayed wire, corroded connection, or damaged wiring harness in the taillight assembly itself (or the wiring leading to it) could be touching the chassis (ground). This creates a low-resistance path, leading to a high current draw and blown fuse. Inspect the wiring thoroughly, looking for any signs of damage, especially near the bulb sockets.
* Short to Ground in the Dash Circuit: Less likely to be the *sole* cause (since it's also affecting the taillights), but a short in the dash wiring (e.g., in a switch, gauge, or other component) could contribute. This would also cause a high current draw.
* Faulty Taillight Switch: A short in the taillight switch itself could draw excessive current even when the lights aren't activated.
* Faulty Instrument Cluster: A short in the instrument cluster (gauge cluster) could also contribute if it shares the same fuse.
* Wiring Harness Damage: Damage to the main wiring harness between the taillight and the fuse box (or the dash and the fuse box) could cause a short. Rodents chewing wires are a common culprit.
* Incorrect Bulb: Using a bulb with a higher wattage than what's specified for your Prizm could also overload the circuit. This is less likely to impact the dash, however.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all wiring related to the taillights and the instrument cluster. Look for any frayed wires, melted insulation, or signs of corrosion, particularly at connection points.
2. Replace the Fuse (Correct Amperage): Make sure you're using the *correct amperage* fuse. Using a higher amperage fuse is dangerous and will not fix the problem; it will just mask the short circuit until something more serious happens (like a fire).
3. Test the Taillights: After replacing the fuse, test the taillights. If the fuse blows again immediately, the short is likely in the taillight circuit.
4. Isolate the Problem: If the fuse only blows when the taillights are on, the problem is almost certainly within the taillight circuit. If it blows even with the taillights off, the problem is elsewhere (dash circuit or wiring).
5. Check the Taillight Bulbs and Sockets: Ensure you have the correct wattage bulbs. Inspect the bulb sockets for corrosion or damage.
6. Professional Help: If you're not comfortable inspecting wiring, it's best to take your Prizm to a qualified mechanic. They have the tools and expertise to diagnose and repair electrical shorts safely. A multimeter can be very helpful in identifying a short.
Remember safety first! Electrical work can be dangerous. If you're not familiar with automotive electrical systems, don't hesitate to seek professional help. Continuing to drive with a short circuit is risky.
