91 Town Car- Engine won't turn over with key

[walt03]

Engine won't crank and turn over when trying to start. Dash Board lights go out as if bad connections on battery. All clean and tight.
Replaced starter and solenoid four years ago.
Could the ignition switch be faulty?
Any suggestions on how to trouble shoot this problem?
Thanks

[Towncar]

Could be a few different things.

• Dead / weak Battery: Does a jump from another battery help?
• Bad Starter / Solenoid: Bench testing should help diagnosis here, or directly apply 12v+ to Starter w/Jumper Cables
• Worn / Defective Ignition switch: Check for 12v + at Solenoid activation connection when Ign.Switch is in Crank position
• Steering column linkage from Key assembly to Ignition switch: Check switch 1st, then if NoGo, this may be a cause
• Neutral Safety switch misaligned / defective: Check switch 1st, then if NoGo, this may be a cause
• Cable / Wire connections @ Starter: Loosen, inspect, then re-tighten all wire and cable connections