I figured I'd take the time to make this since I know a few people that own these, but have never installed them.
First off, whatever the box says: DO NOT DO
But here's a pic, anyway:
(thanks Tyler!)
Instead, here's a wiring diagram to better illustrate things:
I'll describe the wires as they're displayed next to the flasher:
ORANGE - Illumination for the dial
RED - Power for the flasher
YELLOW/BLUE - The box portrays them as left/right, but just consider these as where power comes IN to the flasher
GREEN/WHITE - Like the yellow and blue, left/right doesn't matter so consider these as power OUT to the lights
BLACK - Ground
Inside the cabin, I used a fuse tap to get power through a switch, with the the RED and ORANGE wires connected on the other end (so the light on the dial turns on when the flasher is being used)
The same switch also outputs to the coil-side of a relay I have in the engine bay (thin red line connected to relay terminal 86 on the diagram)
The black wire I just have grounded somewhere under the dash/kick panel area
Regarding the relay, I have wire from the battery with an in-line fuse powering the load input (relay terminal 30)
The load output (relay terminal 87/87a) is a thicker single wire that connects to both the YELLOW and BLUE wires
I forgot to draw it in, but the other side of the relay coil (relay terminal 85) is just grounded
All that's left are the GREEN and WHITE wires.
Doesn't matter which side they power, but run one wire to one light, and the other wire to the other light. Then finish the circuit by grounding the lights locally or onto a common ground.
And that should be about it for the universal install.
If you want a slightly more in-depth S13 install, I have a write-up on Zilvia: https://zilvia.net/f/showthread.php?p=6428762