Where can one find a wiring diagram for a 1989 Plymouth Voyager stereo system?
The 2000 Plymouth Voyager had three engine options for that year, the 2.4L, 3.0L, 3.3L engines. If your vehicle was equipped with the Flex Fuel system or (TLEV) Transitional Low Emission Vehicle, it wouldn't make a difference. The Plymouth Voyager was only equipped with two oxygen sensors, one usually located up at the engine and one usually located down on the exhaust after the catalytic converter.
I am assuming that you want to know how to wire up a new radio replacing the Infinity radio that was in the vehicle. The URL below tells you how to do it in a Plymouth Voyager. http://www.installdr.com/InstallDocs/DCP/PDF/327001.pdf I also found the following URL helpful in explaining a lot abot the infinity system. http://allpar.com/stereo/infinity-guide.html
Try eBay! Just search for "1992 Plymouth Voyager manual", and check the listings for one that includes the Infinity supplement. If the radio is an OE radio, then the information is listed in the owner's manual. Don't have one, get one. Contact your dealer or a salvage yard. If it is a non OE radio, contact Infinity. Mine (a 91) has a separate sound system manual.