As far as I remember from my 85 Aspencade there is not a relay like a car.
It is tied in to your speedometer.
I noticed I was not getting a speed reading on my way to work one morning and I also noticed that my blinkers were no longer working.
Bought and installed a new speed sensor and got a speed reading and my blinkers were working again.
Same thing on my interstate, when my speedo cable snapped my blinkers stopped working.
Good luck and sorry if I have given any wrong info.
The turn signal relays, 1 for the turns and 1 for the 4 ways are located to the left and right rear of the air cleaner if I remember right. Don't know off hand which is which but you can switch them and see if it fixes the problem. The speed sensor has nothing to do with the signals not working, only the self cancel function.