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

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

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