Build a theme car and then the pack to go with it. Remember Dark Rides can also be a sort of mini-monorail too like for instance the 'Peter Pan' ride, suspended boats.
Some Ideas to consider for DR Themes:
Safari Dark Ride with 2 or 4 person Jungle Jeeps.
Peter Pan is public domain ( 1902 ) - Have at it
Snow White is public domain ( 1812 ) - have at it
Captain Nemo - Public Domain
( 1870 ) yes, have at it.
Laff In The Dark - a classic that should be everywhere.
It's A Big World After All ( nothing small about it )
Pirates of the Gulf - Pirates Boat Ride.
Mr. Frog's Wildest Ride - Who Needs Toads.
"Your Parks Tales" - make a generic park dark ride about your park.
"Atomic World" uses multimovers to get your people beyond Inner Space!
Indiana Bones and the Temple of Gloom - An Adventure ride.
Christmas Ride or Holiday Lights. Santa can make a cameo
It is endless and each ride can have it's type of cars, water, monorail, tracked etc.