'The Doors' Robby Krieger Loves Her Madly -- Drops $45K Surprise On Wife

After 40 years of marriage, Doors guitarist Robby Krieger still knows how to light her fire -- dropping $45,000 on a brand new Mercedes SUV for his wife ... and TMZ has a pic of the new whip.

Sources tell TMZ, the former rock star rolled up to a Benz dealership in Long Beach, CA last Monday -- eyeing up a snazzy ML 350 SUV for his wife.

But wife shopping is hard -- and once Robby called to consult his better half ... we're told she shot him down, asking for the slightly smaller GLK 350 instead (see sample comparison below).

We're told Krieger didn't bat an eye -- and immediately catered to his wife's wishes, wiring over $45K to the dealer in exchange for a fully-loaded silver 2012 GLK 350.