Left turn signal hangs up

When I turn on the turn signal they work fine on both sides, if it urn on the parking lights then the left turn signal won't flash, but the right one is ok.
If I shut off the lights they work ok, but then the left turn light stays on all the time when I turn on the lights. Seems after I leave the lights off a while every thing works ok until I turn on the left turn light with the lights on.
Could the turn signal relay be bad.

MBenz Year is 1991, 300E, 87000 miles
Thanks
Norm