This appears to be one of the three 1959 Cadillac Miller-Meteor limo-style endloader combinations (hearse/ambulance) used in the 1984 film Ghostbusters, known popularly as the Ectomobile (as in ectoplasm). In the film it was used to carry the team's ghost-capturing equipment, as well as transporting the Ghostbusters around New York City. Its features include, hypothetically of course, a special pull out rack in the rear containing the staff's proton packs, which facilitates a quick suiting up without having to reach into the vehicle's rear. There are also various gadgets mounted on the top, but their function is never revealed in the movies. Fans speculate that the equipment includes heavy-duty anti-ghost weaponry and defenses. The book Making Ghostbusters describes a deleted scene where a police officer places a ticket on the Ectomobile only to have it instantly flare up into a pile of ashes. Earlier versions of scripts written by Dan Aykroyd for the first Ghostbusters included mentions of the Ectomobile having the powers of interdimensional travel. Right. The shooting script for the movie described the Ectomobile as being black, with purple and white strobe lights that gave the vehicle a "purple aura." But white worked better on screen.
That's all here – with the note that three cars have played the vehicle in the movies, as a third 1959 Miller-Meteor was purchased after the second died during shooting of Ghostbusters II. The black Miller-Meteor seen at the beginning of the first movie was leased and used only for that scene and never converted, but later that one was purchased by the studio and completely converted to the full deal, in white, for touring. It's now in a car museum in Volo, Illinois, and is for sale. The item notes that the original two Cadillac Miller-Meteors are currently sitting in a Sony pictures studios backlot in rapidly deteriorating condition.
Not so. One of them has been moved to Ed's Airport Service, 3127 Ocean Park Boulevard in Santa Monica – a Cadillac specialist – and restoration work is underway. Here 'tis.