The trunk button was never broken.
I fully convinced myself the rear hatch release had failed before discovering the technology known as “the key must be in the ignition.”
A complete electrical diagnosis was almost attempted.
This repair log documents one of the most emotionally devastating discoveries of the restoration so far: I was woefully incorrect.
Symptoms
Troubleshooting attempts
The moment of realization.
Decide the button is broken.
This conclusion was reached almost immediately and with supreme confidence.
Begin troubleshooting process.
The electronics were immediately blamed.
Begin Googling.
Read that the key must be in the ignition for the release button to work. Suddenly the trunk release worked perfectly.
Experience immediate emotional damage.
This one was pretty embarrassing.
Final diagnosis
The rear hatch release system was functioning exactly as designed. The actual issue was the operator not understanding how the system worked.
Final result
The trunk opens correctly, the wagon remains glorious, and I now possess one additional piece of highly specific 1985 Chrysler knowledge.
The learning continues.
Every repair teaches something important. Sometimes the lesson is electrical. Sometimes the lesson is “put the key in first.”