[kipps]

It's not an illumination light. The dash, heater, etc illumination lights are powered with a gray wire, and grounded through a black wire.

Note that one of the wires is pink. Pink wires are universally used for ignition-hot wires. So that light must be controlled by a ground connection through the brown wire.

Looking at Hatzie's wiring diagram for a '86(You can find all the diagrams here), it shows a "check engine" light with two wires. One wire is Pink/black, and the other is listed as brown/white.

The light shows up about two-thirds of the way across the first diagram page on the 86 wiring manual.

If you remove your cluster, you can hold it up to the light, and see what's displayed in each indicator socket. I'm sure you'll find "check engine" or "service engine soon" in one of the holes. If not, the cluster or the harness were replaced at some point.