To the best of my knowledge, they aren't available in the engine bay.
You could run new wires directly from the cluster connector to the t-case switch.
You might also be able to go to the connector for the Electronic 4x4 Module, unplug it and extend the gray and brown/white wires down to the t-case switch. In the 89 Ranger, that module is under the interior trim in the driver side rear of the interior. I don't know whether 87 is the same.