Check the main power distribution unit in the engine compartment first, as it contains high-amperage protection elements responsible for ignition feed, cooling fans, and lighting circuits.
The vehicle uses multiple electrical centers located in the engine bay, trunk area, and passenger compartment. Each unit contains labeled slots arranged by function, separating high-load systems from low-current electronics. Large cartridge-style links typically handle components like ABS, starter supply, and radiator fans, while smaller blade inserts control interior features and signal circuits.
Refer to the cover label for slot numbering and circuit mapping, since each position corresponds to a dedicated system such as fuel delivery, control modules, or climate regulation. Incorrect replacement with a higher rating can cause wiring damage, while a lower rating may lead to repeated failures during normal operation.
Use a multimeter or test light to confirm voltage at both terminals before replacing any protective element. Repeated failure indicates a short circuit or overloaded component, often found near moving parts or heat sources where insulation can degrade over time.
2005 SL500 Fuse Box Diagram with Relay Layout and Circuit Assignments
Use the cover label inside each electrical housing to identify slot numbers and circuit roles before removing any component, as multiple systems share similar amperage ratings but serve different functions.
The engine compartment power unit contains high-load protection elements grouped by system. Positions near the battery typically handle ignition supply, cooling fan motors, and ABS control. These use larger cartridge-style inserts rated between 30A and 60A. Adjacent slots with 10A to 25A ratings support lighting circuits, control modules, and sensor power feeds.
Relay placement follows a functional layout where switching devices sit next to the circuits they control. Cooling fan relays are usually clustered together, while horn and air conditioning compressor relays are placed along the outer rows. Swap relays with identical units from non-critical systems to confirm faults without additional tools.
Inside the cabin, a separate electrical panel manages interior electronics such as window motors, seat adjustment systems, and infotainment components. Each slot is numbered and linked to a specific wiring path. Verify both power and ground at the terminals when diagnosing issues like non-responsive switches or intermittent operation.
Trunk-mounted distribution units handle rear lighting, fuel pump supply, and central locking modules. Inspect for moisture or corrosion, especially around seals and connectors. Burn marks or loose contacts indicate overheating, requiring cleaning or terminal repair before installing new protective elements.
Exact locations of fuse boxes in engine bay trunk and cabin areas
Open the engine compartment and locate the primary power distribution unit near the battery on the right side, secured with a plastic cover and metal clips.
This front-mounted housing contains high-amperage protection elements and relays for major systems. A second unit is positioned in the trunk on the right side behind a removable trim panel, handling rear lighting, fuel delivery, and central locking circuits. Inside the cabin, the interior electrical panel is installed behind a side cover on the dashboard, accessible when the passenger door is open. Each location serves a distinct group of systems, reducing wiring complexity and improving access during diagnostics.
- Engine bay: ignition supply, cooling fans, ABS, lighting circuits
- Trunk area: fuel pump, rear lamps, locking modules
- Cabin side panel: windows, seats, infotainment, dashboard electronics