I have a set I used on my GT long ago (sequential tail blinkerlights). Recently I cleaned up my old harnesses and set them apart. Found them today and took some pics for you.
Looks you could make your own set.
The thing they used is an Aromat 39260 AC powerrelay for 125/250V.
One for each side.It has 4 wires to splice in the Fiero harness:
1 to 12V+ (8amp fuse)
1 to the turnsignalwire
1 to the inner turnsignal light
1 to the outer turnsignal light (delayed)
My guess is that this relay used in a 12V DC car setup acts as a short delay switch. I have not looked into how it is wired at the relay.
Edit: There may be only one relay used because I have 2 wires labeled delay left and delay right. I am a bit confused about how it works for both sides. Anyway I took off the remainder of the tape and this is how it is wired at the relay:
[This message has been edited by Fie Ro (edited 12-01-2021).]