A grown son lives with his mother and is in a wreck with inadequate liability available from the adverse driver. Can he make a claim under his mother’s UM, even though his car is not on that policy?

It will depend on the language of the Mom's UM policy. See: Conner v. American Commerce Insurance, 2009 OK CIV APP 61, 216 P.3d 850: holds that a policy provision excluding from uninsured motorist (UM) coverage a named insured who is injured while occupying a vehicle he owns but which is not covered by UM coverage is a valid exclusion. See also: Morris v. America First Ins. Co., 2010 OK 35, 240 P.3d 661, confirming ruling in Conner but finding an exception where the insured in question (the son) has UM coverage under another policy.