When you purchase a new car it is important to remember who is on title. Banks and lessors will never let you forget when they are on title. They will even force their own (very expensive) insurance when they do not get evidence of insurance from you, but a co-signer may not know that they need to be listed as a registered owner or additional interest on your insurance policy.
It is important to know that insurance follows the car and not the driver. This means that if a co-signer is not listed on the policy where the car is insured, that co-signer is not insured for that auto. If that car is in an accident, regardless of the driver, and the injured party sues the registered owners there is no coverage for that co-signer/ registered owner if that person is not listed on the policy that insures that car.
They may have their own auto policy but if the car in question is not listed on that policy, no coverage. So it is important that all registered owners are listed as either a driver or additional interest (if they are not going to drive that car). There is no charge to list someone as an additional interest. If the co-signer is not going to be listed as a driver, the insurance company may ask you to exclude them from the policy before they add them back as an additional interest.
This article(s) represents the views and opinions of Garrett Parkinson and not the Insurance Companies that he represents or illustrates in his articles.