Peugeot 205 - indicators not working, everything else is including hazard lights

Peugeot 205 Sceptre (L reg.) Indicators not working, everything else is working including hazard lights. The black relay buzzes but does not click and the lights do not blink on and off. however the flasher does work which operates the black relay. This is an intermittent problem which occurs without warning. No pun intended. There is an after market trailer hitch fitted which has been spliced into the rear light wiring. Any help would be greatly appreciated. I thought that the coil of the black relay may not be getting enough voltage to properly turn it on but that is difficult to test. I do have a multimeter. I suppose that if the coil voltage is low it would point toward the switch on the steering column.