An eBay seller has a nice loco for a good price but he doesn't know the power source or operating. I have tried the Marklin website and others but cannot find the into. I run ac analog. Does anyone know?

A DC loco can be converted to ac 3 rail, if an ac field coil is available, and a pickup shoe can be fitted. However, only on rail will be grounded as the wheel sets are insulated. Sometimes they can be changed, but if your rail joints are all tight, it will run fine. You will need to install a reversing unit for analog operation. If you want to make it digital, the decoder does it. This also requires a 5 pole armature and a field magnet upgrade. It's much simpler to convert an ac loco to DC. The existing motor will run, maybe a bit faster.