Post model number for Snapper SX825.
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A number or letter is missing in model number. You can go to Snapper website to download wiring diagram, etc. Check all electrical connections for corrosion,rust, and being tight, especially all ground connections.
If corrosion or rust is present, use a wire brush and be sure to use safety glasses and gloves. Bacon soda mixed with water will help get rid of corrosion.