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Once you remove the engine that wiring harness is pretty straight forward. There are two main harnesses. One for the battery and one for engine controls. You can honestly pull the motor with the harness installed, however for ease of operation I prefer to get it out of the way since it likes to get snagged on silly stuff. Like uberstang said, there is no reason to re-use your old harness if you have the new one, especially if you want a clean install. Since it won't have clips in the right places for the 4v engine.