Volvo 740 turn signal problems

[DOWL1006]

the left turn signal on my 1991 Volvo 740 does not work when the head lights are on, and the green turn arrow on the dash is cont. lit.....when the head lights are off the turn signal works and the green turn arrow and bulb out indicator both flash when turn signal is engaged...i checked the turn signal bulb and it looked to be in good order, filaments intact and i clean the connection, but this did not resolve, please advise....thank you in advance for your help