Johnson Pump Ultima Switch 36303 connections

Ultima Switch detects water with sealed field-effect sensors and has no moving float. The SPX FLOW US specification for 36303 gives a 20 A rating; this catalog deliberately models only the 12 V, 20 A application. Manufacturer literature for some international 34-36303 versions limits 24 V switching to 10 A, so verify the exact label before reusing a 12 V design on 24 V. The switch’s rating is not its own consumption or a recommended fuse.

Brown with white stripe connects to protected battery positive through the chosen pump’s fuse. Plain brown connects to pump positive; pump negative goes directly to the negative bus. Do not treat a wire’s brown color or a confusing minus annotation as permission to connect the output to battery negative. Join and seal conductors above the highest expected water level. Size extensions for pump demand and the complete outgoing-and-return route.

The mounting holes face downward and the sensing circles remain vertical. Place the switch close to the pump at or above its base, clear of objects that can falsely cover the sensing area. A bonded mounting block avoids penetrating the hull; the manual describes a block at least 3/4 inch thick. The switch turns on at approximately 2 inches (50 mm) and off at 3/4 inch (20 mm); the published delay helps reject splashes rather than guaranteeing the bilge remains completely dry.

For the manual’s bench check, hold fingers over both raised sensing circles for about ten seconds. The pump should run; removing only the upper finger should leave it running, and removing both should stop it after the delay. Then test with water in the installed bilge and verify actual pump discharge. The catalog states simply show a conducting or open path; they do not reproduce timing or detect contamination. Clean and retest the sensing face during regular bilge maintenance.

Johnson Pump installation manual, IB-116 R05, November 2018; 52288-00 R01; English installation section pp. 8–12; supplemental SPX FLOW Bilge Pump Switches specification p. 2. The original PDF is retained in the marine source ledger. The drawing represents the identified electrical interfaces; it does not simulate the equipment’s mechanical performance, radio signals or fluid system. Unpublished connector ampacity and startup current remain unspecified.