Sierra 18-5881 Switch Box for Mercury 120 HP 4-Cylinder Inline Outboards with ADI Ignition

The Sierra 18-5881 is an ignition switch box engineered for Mercury 120 HP four-cylinder in-line outboards equipped with ADI (alternator driven ignition) ignition systems. It serves as the central switching component in the ignition circuit, controlling current flow to the ignition coil and related components so the engine fires reliably in the demanding marine environment. The unit operates on a 12-volt system at a 5-amp current rating with a normally open, single-circuit contact configuration, and connects into the harness through a clamp-style connector.

Construction uses stainless steel and bronze contact materials chosen for resistance to corrosion from moisture and salt exposure, and the housing measures 9.8 x 4.6 x 0.9 inches. Sierra builds this switch box to meet or exceed the performance of the original equipment part it replaces, supplying the same fit and electrical function expected by Mercury 120 HP owners running the affected engine serial ranges.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-5881
• Item Type: Switch Box
• Application: 4-cylinder in-line outboards with ADI ignition systems, 120 HP
• Operating Voltage: 12 Volts
• Current Rating: 5 Amps
• Contact Type: Normally Open
• Circuit Type: 1-way
• Connector Type: Clamp
• Contact Material: Stainless Steel, Bronze
• Item Dimensions: 9.8 x 4.6 x 0.9 inches
• Weight: 1.17 pounds
• Manufacturer: Teleflex Marine
• Warranty: Limited Warranty

Fitment

• Mercury 120 HP, 1991D-1992C, 1993, 1994, Serial Number E000001-E093699
• Mercury 120 HP, 1995, Serial Number E093700-E138599
• Mercury 120 HP, 1991-1992, L-Drive

Frequently Asked Questions

What engines does the Sierra 18-5881 switch box fit? It fits Mercury 120 HP four-cylinder in-line outboards equipped with ADI ignition systems, covering serial number range E000001-E093699 for 1991D-1992C, 1993, and 1994, serial range E093700-E138599 for 1995, and the L-Drive version for 1991-1992.

Is the 18-5881 a genuine replacement or an aftermarket copy? Sierra part 18-5881 is engineered to meet or exceed the performance of the original equipment switch box it replaces, providing the same fit and electrical function for the applicable Mercury 120 HP outboards.

What voltage and amperage does this switch box handle? The 18-5881 operates on a 12-volt marine electrical system and is rated for 5 amps of current.

What are the physical dimensions of the switch box? The Sierra 18-5881 measures 9.8 x 4.6 x 0.9 inches.

How much does the 18-5881 switch box weigh? It weighs 1.17 pounds.

What material are the switch contacts made from? The 18-5881 uses stainless steel and bronze contact materials, chosen for resistance to corrosion in the marine environment.

Does the 18-5881 fit L-Drive Mercury 120 HP outboards? Yes, it fits the 1991-1992 L-Drive version of the Mercury 120 HP outboard in addition to the standard in-line configurations.

What type of connector does the switch box use? The Sierra 18-5881 connects through a clamp-style connector.

Is this switch box normally open or normally closed? The 18-5881 uses a normally open contact with a single-circuit (1-way) configuration.

Who manufactures the Sierra 18-5881 switch box? It is manufactured by Teleflex Marine under the Sierra brand.

What ignition system does the 18-5881 work with? This switch box is built for ADI (alternator driven ignition) systems used on Mercury 120 HP four-cylinder in-line outboards.

What comes in the box when I order the 18-5881? You receive one Sierra 18-5881 switch box.