As I am licensed in Florida and Vermont, I cannot comment specifically on Wisconsin law. However, generally, if you are found to be negligent and were driving your vehicle too fast for conditions and caused the accident, you can be responsible for any judgment which the other party obtains against you. It is always advisable to carry liability insurance when you are operating any motor vehicle.
Lars is certainly correct regarding auto insurance. It's for situations exactly like this.
In Wisconsin if you are found to be 50% or more at fault then you are responsible to pay that percentage of the damages. If the other car is found 51% at fault then that driver will not be able to recover.
Have you considered filing a counter claim for the damage to your vehicle? Depending on the facts it may be a 50/50 split where each person's damages would, in essence, off set.
I know of a number of attorneys who may be able to help out.
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