Open the side dashboard cover on the driver side and compare each labeled slot with the printed legend before removing any protective insert. This prevents disconnecting the wrong circuit and avoids additional electrical faults.
The interior distribution unit handles systems like lighting, infotainment, and control modules, while a second unit under the hood manages higher loads such as cooling fans and engine electronics. Each position is marked with a number and abbreviated function, requiring careful matching.
Use a multimeter to verify continuity and voltage rather than relying only on visual inspection. A metal strip inside a protective element may appear intact but fail under load. Check both sides of the slot for voltage while the system is active.
Relays positioned рядом with the distribution units control switching for headlights, fuel delivery, and auxiliary systems. Swap identical relay units between circuits to identify faults quickly.
Inspect wiring harnesses connected to the panel for loose connectors, corrosion, or worn insulation near mounting points, as these issues often lead to intermittent electrical problems.
Exact location of interior and engine compartment fuse panels in C300
Open the driver side dashboard end cover to access the interior electrical distribution unit mounted on the side of the instrument panel.
This cabin-mounted unit sits behind a removable trim piece secured with clips. Inside, rows of protective inserts and relays are arranged with labels for lighting, infotainment, and control systems. Use the printed legend on the cover to match each slot with its function.
For the engine compartment, lift the hood and locate the main power distribution unit near the battery.
- Enclosed in a sealed plastic housing
- Secured with locking tabs on both sides
- Contains high-amperage circuits and relays
- Layout printed inside the lid for reference
Press the side tabs to remove the cover and inspect internal components, then ensure the housing is tightly closed after checks to prevent moisture and dirt intrusion.
How to read fuse diagram labels and match circuits to vehicle systems
Check the legend printed on the panel cover and match each abbreviation with its corresponding system before removing any component.
Labels are usually shortened to save space, so understanding common abbreviations is required. For example, “ACC” refers to accessory power, while “IGN” connects to ignition-controlled circuits. Compare these labels with vehicle functions such as lighting, audio, or control modules.
Each slot includes an amperage rating that indicates the maximum current allowed. Always match the same rating when replacing a protective insert to avoid circuit damage or repeated failure.
| Label | Meaning | System |
|---|---|---|
| ACC | Accessory | Radio, power outlets |
| IGN | Ignition | Engine control, dashboard |
| H/L | Headlamp | Front lighting |
| ABS | Anti-lock braking | Brake system |
Relays are often shown рядом with these labels and control switching for higher-load systems. Identify them by their position and symbol markings, then match them to functions like headlights or fuel delivery.
Trace circuits by following the numbering system printed near each slot. This numbering corresponds to wiring paths leading to specific components.
Use a multimeter to confirm voltage at the identified slot before assuming a fault, ensuring the correct circuit is being tested.
Cross-check with the owner manual if labels are unclear, especially for less obvious abbreviations or shared circuits.
Step by step checks for blown fuses and relay related electrical faults
Remove the suspected protective insert and inspect the metal strip inside, then confirm continuity with a multimeter instead of relying only on visual inspection.
Set the multimeter to continuity mode and place probes on both terminals of the removed insert. If no tone or reading appears, replace it with one of identical amperage. Never install a higher-rated replacement, as this can lead to wiring damage under load.
Next, test the relay controlling the affected system by swapping it with another identical unit from a non-critical circuit. If the issue shifts to the swapped circuit, the relay is faulty and should be replaced.
Check voltage at the relay socket and insert terminals while the system is active, then inspect wiring connections for looseness, corrosion, or heat damage that may interrupt current flow.