Ignition Switch 6 Terminals 3 Pos 87-17009A5

Function and Technical Context

The 6-terminal, 3-position ignition switch is part of the primary ignition circuit in Mercury Mariner outboard marine engines, acting as a control element between the battery, the ignition module, and the electric starter motor. Its three positions—off, on, and start—allow the operator to safely manage the complete engine startup and shutdown sequence from the control panel or helm console. With 6 terminals, this key switch simultaneously manages multiple auxiliary circuits (instrument power, electric choke, ignition cutoff) with a single operation, which is essential in installations with compact control panels. A deteriorated switch or one with corroded contacts can prevent starting, cause intermittent ignition cutouts during navigation, or generate false contacts that damage engine electronics.

When to Replace This Part?

The most common symptoms of a worn-out starter switch are: difficulty turning the key, starter motor that does not respond despite a charged battery, sudden engine cutouts during navigation, or ignition that does not activate in the correct position. The moisture and salt-water corrosion typical of the marine environment degrade internal contacts more rapidly than in terrestrial applications, so it is advisable to inspect the switch at each seasonal maintenance interval and replace it at the first sign of electrical intermittency. Replacing the key switch preventively is a low-cost measure that avoids being stranded without starting capability in open water or in a foreign port.

Mercury / MerCruiser

Equivalent Manufacturer References