A possible alternative solution--
On the Saabs I've had, the headlights (but not the parking lights) are wired through the ignition, so you can't leave them on. To the gurus in our group--how complicated would the rewiring to do that be?
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)