Sorry if I totally missed this while I was searching, but I just bought my 1989 GTU and the right turn signal doesn't work at ALL. there is no noise to indicate out bulbs and neither the dash nor the outside signals light. If I under stand right sometimes you have to replace the board in the ECU but it didn't seem like the same problem from the symptoms listed on the threads... again sorry if I missed it I'm a newbie

 

I would start by checking proper continuities in the turn switch (outlined in the FSM).

That board that you speak of is for the CPU (body computer), not ECU. The CPU is located by the driver's left foot.

 

If you take out the flasher board from the CPU, you can resolder some of the connections and it might fix your problem (it did for me).