When the Mercruiser 470 Voltage Regulator fails

The Mercruiser 470 is an all Mercury designed engine and as a result there are some funky designs which results in expensive repairs for rare parts. One of the funky design issues with the Mercruiser 470 is the Voltage Regulator. Rather than incorporating an Alternator with a built-in voltage regulator, the Mercury Engineers designed the charging system for the Mercruiser 470 with a Stator and external voltage regulator, similar to the system used in Outboard engines. The Voltage Regulator for this engine has Fresh Water / Coolant running through to cool it.

When the Voltage Regulator goes, it usually goes out in a very noticeable way. Many times when they go, internal components of the Voltage Regulator burn up, resulting in smoke in the engine compartment and the obvious smell of an electrical fire. The Voltage regulator may still work, but the reading may be inaccurate.

In my case, I was taking my 17ft Formula One out for Water Skiing one recent morning, when we smelled an electrical burning / fire when I was cruising at 3500 rpms. I looked down to the Voltmeter and it was charging at 16 Volts. As I increased RPMs, the volts increase to 18 volts. When I pulled back, the Volts then read 13 Volts. The Voltage Regulators are not very reliable and are expensive. If your systems is charging at less than the 13.5, I was told that it’s ok. Charging over 13.5 could cook a battery and cause a fire.

I tested the volt gauge with a digital Multimeter I bought at Radio Shack a few years back. With the meter, I tested the input to the Volt Gauge and found as the engine increase in RPM, the Meter and Volt Gauge had the same readings.

To replace the Voltage Regulator, I have 2 options. One is to purchase for about $400 a new Voltage Regulator or Buy an Alternator conversion kit for the Mercruiser 470 at $450 to $600. The Alternator kit will by-pass the Stator and fresh water cooled Voltage Regulator for a common Alternator with internal Voltage Regulator System. The Alternator kit is the way I wanted to go, however there is very little room in front of my engine, thus restricting me from installing an Alternator in front of the Engine.

Though the Mercruiser 470 Voltage Regulator is very expensive, the good news is to replace it, there is very little labor involved. All you need to do is remove the 2 yellow Stator wire, the Red hot wire an Orange lead output wire. Then you need to take out the 2 top bolts and 1 bottom bolt, detaching the Voltage Regulator from the block. Then you need to remove on both sides the fresh water hoses. At this point, it might good to have at hand two rubber stoppers to plug the Fresh Water hoses, so that you don’t lose too much coolant. If you got this far, you should then be able to figure out the rest in re-installing of the new part.

Mercruiser 470 Voltage Regulator

If you need help in the installation of the Mercruiser 470 Voltage Regulator 99502A13 or 99502A12, please refer to the link below:

Wiring Diagram of MerCruiser Voltage regulator.pdf

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