Only brown/pink I see in the diagrams just shows it as part of the key on circuit to the fuse panel
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Ignitionsystem_1989_2_3.JPG
Upper left of diagram, it looks like it is supplying power to a fuse or relay with key in start or run position, so should be a Hot wire with key on, not a supply wire as you described, so this diagram may not apply to the '86.
Do you have a test light or meter to test that wire?
To see if it has power with key on.
Older starter solenoids had 4 posts, two larger ones and two smaller ones.
The smaller ones are labeled "S" and "I"
"S"(start) is used to activate the solenoid, so the starter motor
"I"(ignition) is used to send the Coil 12v power only when engine is cranking to increase the spark to start the engine.
Coils tend to overheat on constant 12v power so a resistor is often used to lower the voltage to 8v while engine is running.
This resistor can be a "resistor wire" or a "ballast resistor".
The "I" post was eventually dropped on solenoids and this "12v to coil wire" was moved to the larger post that has the larger wire that went to the starter motor, so same function but without extra post, when start motor gets 12v via the solenoid the coil gets 12v via the solenoid.
From your description it reads like this brown/pink is the coil power,
"engine cranks without it connected"
"engine starts with it connected to 12v"
"engine dies when 12v is cut"
Is there a relay or fuse panel this wire could have been pulled out of?
I am not familiar with the 1986 engine compartment lay out.
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