Well, I don't have an 1100GK, so I am using an 850G(k) schematic.
It's actually
the one that is on BassCliff's site as a very good diagram with colors.
Except for the few differences that came with the '82 models, it still applies very well.
Tracing back from the tail light, it is powered by a brown wire.
The brown wire comes from the ignition switch.
In the PARK position, it is fed by a red wire that comes from the MAIN fuse.
In the ON position, it is fed by a gray wire that comes from a connector that is fed by an orange wire with a red stripe.
That orange/red wire also feeds the yellow/white wire that goes to the headlight beam selector switch to power the headlight.
The orange/red wire comes directly from the end fuse, which is LIGHTS, and powers the headlight AND the tail light.
In that same wiring diagram, if you follow the second fuse from the end (SIGNALS),
you will find that it is an orange/green wire that powers the turn signal control unit, turn signal relay,
brake lights, horns, fuel gauge regulator, neutral light and oil pressure light (but not the tail light).
Just for the sake of completion, the third fuse is the IGNITION fuse. It has an orange white wire that goes first to the "kill" switch, then to the starter button, coils and ignitor.
EDIT: I just took a good look at the
1100GK diagram that is on BassCliff's site. It is one of several that I have found to have a mistake in it.

To show you the mistake, please follow along with me here:
Start at the battery, follow the red wire to the MAIN fuse, then continue to the ignition switch. When the switch is in the ON position, it appears that the red wire will be connected to a GRAY wire. Follow the gray wire, you will see that it powers the front running lights (in the turn signals), the dashboard lights and the license light,
but nothing else.
Now go back to the problem at hand: powering the tail light. Let's follow it from the light to the source in that diagram. Follow the brown wire from the tail light to the ignition switch, it appears to be powered by the orange wire. Follow the orange wire, you will see that it ends at the fuse box, where it is connected to three fuses.
The mistake in the diagram is that the orange wire and the gray wire are reversed in the ignition switch. The red wire from the MAIN fuse should be connected to the orange wire, and the gray wire should be connected to the brown wire.
.