Small Engines (Lawn Mowers, etc.): regulators, regulator rectifier, electric clutches

Question
QUESTION: i have just bought a new B & S 18.5hp motor to go on my lawnmower and the engine plug colors does not match up to my mower. can you tell me how it is supposed to be wired? I know what/where all the colors coming from the mower is, just don't know anything about the wires coming from the motor

ANSWER: One or two wires?

The engine produces AC current and it has to be changed to DC current.  If there is one wire it goes to a diode in the harness that goes to the battery and the electrical system.

If there is two wires they will go to a regulator rectifier to basically do the same thing.  The wires from the harness will then hook to the regulator rectifier.  The regulator rectifier changes the AC to DC.  Larger more complex systems use the regulator rectifier and tractors without electric clutches, etc. use the more simple system.

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wires from motor   QUESTION: There are 2 sets of wires coming out of motor (black and red and gray and black). Does the yellow regulator wire hook into the engine plug that will connect it to the black (of the red and black)? There was a connector in the harness that we attached the red wire to. Or do we even have to worry about the regulator with this motor?

Answer
This sounds like a B & S dual circuit charging system.  One set is for charging the battery and the other is for the rest of the system.  If dual circuit the lights only work if the engine is running.  One set goes to the bridge recfier and then on through the rest of the system.  One of these has to go to ground to ground the ignition system when you turn the tractor off.  Go to the B & S website and see if you can find the specifications for the tractor.  If this is a regulated system it should have come with the regulator. I know I'm rambling but with the wires you say there is coming off the engine one charges the battery which color one, I don't know.  Changing out an engine with different type engine is a difficult task.  What is the exact replacement engines wiring system?  Compare that to the one you have and it may answer all for your questions.Sorry I wasn't more help.