After we'd made our left turn under the power lines and across the old rock-lined aqueduct, it was a short distance until we were back on the main trail leading up the canyon.
The trail heads back toward White Mountain Ranch for a short distance, and then makes a right-hand u-turn. Once you've made this right-hand u-turn you're following the main route.
At the u-turn's apex you can see the old two-track coming up from the hydroelectric plant at White Mountain Ranch.
For good measure, I walked down the old route and snapped a photo of the 4Runner on the new trail.
Above the 4Runner you can see the Spark Plug mine area as a cluster of bright-colored rock outcroppings in the canyon above.
The difficulty in finding the main trail means that only very stubborn (or very determined) off-roaders will successfully make the journey up to the Champion Spark Plug Mine. Hopefully, those same stubborn folks will also be stubbornly respectful of the irreplaceable historic treasures waiting up the canyon.