I had similar problem recently on my 89 244 dl.Turned out to be dirty contacts where the wiring harness plugs on to the drivers side rear light assembly.The passenger side piggy backs off of it so neither reverse light worked.I simply cleaned up the contacts and stuck a little piece of foil on there for added conductivity, works like a champ.Could be your reverse switch too , or wiring, but I would check the simple stuff first. Good Luck!