My battery(positive side) keeps getting corrosion on it. The car just hit 20,000

I have the same issue and the dealer is suggesting to change the wiring harness. I had the dealer do regular oil changes and they never reported any corrosion on the battery terminals. I even jump started my other car using my highlander and never observed the corrosion. It's surprising to see so much corrosion. I am wondering if Toyota put in a defective battery...