Most importantly however is the 15 pin ‘remote' connector on the back of all of the older analog sets. This remote plug in connects to either a wired remote box that has the brightness, contrast, sharpness, input selection and color and tint controls on it. The other option for this connector is to run a 15 pin wiring harness to an RCVDS 4 Barco video switcher that also has these controls right on the switcher.
The point is, a lot of these projectors are sold surplus without the switchers or plug in remotes. The set will power up but no picture will be displayed without anything connected to this 15 pin port. RCVDS switchers can be found on eBay, but the plug in remotes are hard to find.