Zero Turn Mowers

I have a RZ4623. Approx 3 years old. This season it has suddenly started blowing the 20A fuse that sits between the switch and ground. The engine starts and runs for perhaps 3-5 seconds and then the fuse blows. It is a strong enough short to burn some of the plastic of the fuse and scorch the fuse wire at the fuse holder end. I replace the fuse and re-start the engine and mow for several hours without a problem. Next time I want to mow, chances are the 20A will blow upon starting. I have recently replaced the starter and it has been working great. The fuse doesn't blow until after the mower starts. Ideas as to where to start looking for the short....thanks.