Law Lemon Wisconsin

I bought a car about a week ago from a dealer. I was told that the car came with some minor defects such as leaks, etc. One problem I was told about was that the ABS light would come on but I was told that there was no ABS problem and that it was only a defect with the gauge. The buyers guide on the window listed no problem with the ABS. I had the car checked out by another mechanic and I was told that the ABS did not work at all and it would cost a lot of money to fix. The dealer told me he would fix it at a 20% discount.
So, what should I do? Is there a lemon law in this case?
And if the lemon law doesn’t apply in this case would it be cheaper to get it fixed at the dealer or at another mechanic?