The Mercury 40-Amp Voltage Regulator Kit from Buckshot Racing #77 is a complete replacement for the original water-cooled charging-system regulator used on selected Mercury and Mariner V6 two-stroke outboards.
 
The kit is manufactured in the USA by CDI Electronics 194-1873, now Sierra 18-99442, and replaces the obsolete Mercury 18736 A8 to A21 40-AMP regulator assemblies.
 
This regulator is intended primarily for 1989–1991 Mercury and Mariner 135, 150, 175 and 200 HP V6 outboards equipped with the factory 40-amp charging system. Applications include selected 2.0L, 2.4L and early 2.5L V6 engines, depending on model, serial number and original charging-system configuration.
 
Complete 40-Amp Regulator Replacement Kit
 
The Buckshot Racing #77 kit includes the 40-amp voltage regulator, mounting plate, gasket, mounting bolt and spacer hardware required to replace the original Mercury regulator assembly.
 
The CDI 194-1873 / Sierra 18-99442 is specifically designed for Mercury’s early high-output 40-amp charging system. It should not be confused with later Mercury dual-regulator systems or other regulator designs that may appear similar.
 
Mercury OEM Part Number Cross References
 
The CDI 194-1873 / Sierra 18-99442 replaces several Mercury OEM regulator numbers used as the charging system was updated, including 18736A8, 18736A11, 18736A14, 18736A15, 18736A20 and 18736A21.
 
These earlier Mercury part numbers are important when identifying an original regulator because many engines still have older factory assemblies installed. Mercury eventually superseded several versions to 18736A21, which is now discontinued.
 
Mercury 2.0L, 2.4L and 2.5L Applications
 
Common applications include Mercury and Mariner V-135, V-150, V-175 and V-200 engines equipped with the original 40-amp charging system. This regulator family is also associated with selected XR4, Magnum II, XRi, 175 EFI and 200 EFI engines from the late 1980s and early 1990s.
 
Some early 2.5L 200 HP engines also used this system. Because Mercury changed charging-system designs within the same horsepower and model families, fitment should be verified by the existing regulator part number, stator configuration and engine serial number rather than horsepower alone.
 
How the Mercury 40-Amp System Works
 
The stator produces alternating current as the flywheel rotates. The regulator/rectifier converts that AC output into DC charging voltage and controls the voltage supplied to the battery and electrical system.
 
A failing Mercury 40-amp regulator can cause low charging voltage, no battery charging, erratic tachometer operation or excessive charging voltage. Overcharging can damage batteries and onboard electrical equipment, while poor connections can generate heat and damage both the regulator and wiring.
 
Before installing a replacement, inspect the stator leads, battery cables, grounds and charging-system terminals for corrosion, loose connections or overheated wiring.
 
Verify the Stator Before Ordering
 
The regulator must be matched to the correct Mercury 40-amp stator system. Some later service conversions use different stators and dual-regulator configurations, so the existing charging system should be identified before parts are ordered.
 
If the engine still retains the original 18736-series regulator setup, the CDI Electronics 194-1873 / Sierra 18-99442 provides a direct solution for maintaining the original system configuration.
 
Made in the USA Replacement
 
The CDI Electronics 194-1873, cross-referenced as Sierra 18-99442, provides a modern replacement for Mercury’s increasingly difficult-to-source early 40-amp regulator system.
 
For compatible Mercury and Mariner 2.0L, 2.4L and early 2.5L V6 40-amp engines, the Buckshot Racing #77 kit includes the regulator and required mounting hardware to replace Mercury 18736A8, 18736A11, 18736A14, 18736A15, 18736A20 and 18736A21.
 
Contact Mike Hill with technical questions at 714-697-1716