W123 Rear Light Problems

[rmmagow]

The rear lights on my 83 W123 Diesel are working very strangely. With the headlights turned on when I use the signal for a right hand turn the yellow light on the right blinks as does the red light next to it as well as the white back up light on the left side. The yellow and red blink alternately while the white back up blinks with the red on the other side. Left turn signal works as expected, just blinking yellow lights. When turning on the 4-way flash if headlights are off all is OK, with lights on I get the similar strange behavior in the rear. Wth the headlights on, pressing the brake pedal will cause a very slight glow in the right-turn signal in the dash. Also when putting the car in reverse with the headlights on will cause a bright glow in the right turn signal in the dash which gets brighter when pressing the brake pedal. What could be causing this? Bad flasher unit? Is there only one flasher for both directionals and flashers? Could there be something wrong with the headlight switch? The rear bulbs appear to be the correct type and the cruise control works fine which I know uses the rear lights for signaling. Any advise is greatly appreciated.