Small Engine Troubleshooting Problems? Ask a Mechanic Now.
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Wire colors? Where are the wires coming from? Black wire would be kill wire. But What did original have foe charging system?
What did it have for a charging wire! Any voltage regulator?
Here is the Briggs manual on engine swaps, See the various wiring schemes.
The typical brings engine just has a black kill wire, the other wires are the charging system.