Regulator Rectifier: 5 Checks Before You Order

A failing regulator rectifier shows up as a flat battery, blown bulbs or a battery that boils. Replacements often look the same from the outside: a finned aluminium box with a plug or two. That is why so many wrong ones get ordered. This guide covers the checks we recommend before you buy, using real examples from our own range.

Prefer to read? The full guide is below.

First: is it really the regulator?

1. Start the engine and measure the voltage across the battery terminals.
2. Compare the reading with the charging voltage in the listing's technical specs. For most of our units that is 14.5 V ± 0.5 V. Some older designs differ, for example 13 V ± 0.5 V on the Polaris 500 unit for 1997–2003.
3. Well above 15 V: the regulator is overcharging and needs replacing.
4. Voltage stays low: test the stator's AC output as well. A new regulator won't fix a failed stator.

Check the connector too. Melted or corroded plugs are common on older machines. That is why many of our regulators come with the opposite connector for the harness side.

Check 1: Match the part number

Look for the number stamped on your old unit, then find it in the cross-reference table on the listing. For example, our Yamaha Kodiak 400 regulator is listed against:

• Yamaha 4GB-81960-00-00 (also written 4GB-81960-00)
• Shindengen SH535-12

Check 2: Plugs, pins and wires

Count the plugs and pins on your old regulator. If the count doesn't match, the new unit won't plug in.

Check 3: The type

• AC regulator: controls the AC lighting circuit only and does not charge a battery. Example: the single-wire AC regulator for the Honda CRF 50 and similar machines.
• Regulator rectifier: converts the stator's AC output to DC, regulates the voltage and charges the battery.
• Single-phase or three-phase: this has to match your stator.
• MOSFET: runs cooler than a traditional diode-style unit. The plugs still have to match. See, for example, our three-phase MOSFET regulator RM30506H.

Check 4: Mounting holes and size

Measure the distance between the mounting holes, centre to centre:

• 55 mm: Kawasaki Bayou unit
• 67.5 mm: Yamaha Kodiak 400 unit
• 82 mm: later Polaris MOSFET units

Check that there is room for the new unit, too. The Polaris 500 regulator for 1997–2003 measures 64 × 74 mm. The MOSFET unit for 2007–2010 measures 107 × 112 mm.

Check 5: The exact model and year

The same machine can use completely different regulators depending on the year. The Polaris Sportsman 500 is a good example:

2010 appears in two ranges, so for a 2010 machine check the part number and count the pins.

Quick checklist before you order

1. Regulator at fault: battery voltage measured, stator checked if the voltage is low?
2. Part number: is it in the cross-reference table?
3. Plugs, pins and wires: does the count match?
4. Type: AC regulator or regulator rectifier? Single-phase or three-phase?
5. Mounting and size: hole spacing, and room for the unit?
6. Model and year: does your exact machine appear in the fitment guide?

FAQ

Can a bad regulator damage my battery?
Yes. An overcharging regulator can make the battery gas, swell or boil. An undercharging one leaves it flat. Measure the battery voltage with the engine running.

Is a MOSFET regulator better?
A MOSFET regulator runs cooler than a traditional diode-style unit, which usually means a longer life. It only fits if its plugs, mounting and type match your machine.

Is the connector included?
Many of our regulators include the opposite connector for the main harness side. Check the listing's "What is included" section.

Not sure which regulator you need? Send us your part number or a photo of your old regulator before you order. You can also browse all regulators and rectifiers. More buying guides: starter motors and power trim & tilt motors.