Possible Causes:
* Worn Ignition Switch: This is the most likely culprit. Over time, the internal components of the ignition switch wear out, preventing it from properly engaging the starter.
* Broken Ignition Cylinder: The part where the key goes might be damaged or broken internally.
* Wiring Issues: A problem with the wiring harness connecting the ignition switch to the starter solenoid could prevent the starter from receiving power. Look for broken or corroded wires.
* Faulty Starter Solenoid: While less likely given your description, a faulty solenoid could also prevent the starter from engaging. This would usually manifest as a clicking sound when you turn the key.
* Low Battery: Although it spins freely, a very weak battery might not provide enough power to engage the starter even if the ignition switch is working.
Troubleshooting Steps:
1. Check the Battery: Make sure your battery has a good charge. Test its voltage with a multimeter. A low voltage reading could be the problem.
2. Listen Carefully: When you turn the key, do you hear *any* clicking sounds from the area of the starter (usually under the hood, near the engine)? A clicking sound usually points to a low battery or a faulty starter solenoid. The absence of *any* sound strongly suggests an ignition switch problem.
3. Inspect Wiring: Look for any obvious damage to the wires going to the ignition switch and the starter solenoid. Look for corrosion, breaks, or loose connections.
4. Test the Starter Solenoid (Advanced): If you're comfortable working with car electrical systems, you can try bypassing the ignition switch and directly powering the starter solenoid to see if the starter works. This involves direct contact with the battery terminals and is potentially dangerous if done incorrectly. If you are unsure about this step, do not attempt it and take your vehicle to a professional.
Fixing the Problem:
* Replace the Ignition Switch: This is the most likely solution. It requires some mechanical skill and familiarity with automotive electrical systems. You'll need to remove the steering column shroud (usually involves removing the steering wheel or some components beneath), unplug the old switch, and install a new one. A replacement switch is relatively inexpensive.
* Replace the Ignition Cylinder: This might be necessary if the key is worn or the cylinder itself is damaged. This is also a more involved process.
* Repair or Replace Wiring: If you find broken or corroded wires, they'll need to be repaired or replaced.
Recommendation:
Unless you have experience working on car electrical systems, it's best to take your 1985 F250 to a qualified mechanic. The ignition switch replacement is not overly difficult, but improper installation could lead to further damage or safety hazards. A mechanic can properly diagnose the problem and perform the necessary repair. Replacing the ignition switch is the most probable solution.
