History on a '94 with a "won't crank" issue:
For two days, I noticed that starter seemed to crank very slowly/weakly.
On third day, just a click. Thought it was a battery problem, and when jumped with another battery, it started just fine.
Replaced battery on day four, to no effect. Just a click.
On day five, removed starter motor and took to shop for testing. Starter tested good.
Reinstalled starter.
Found insulation damage on positive cable where it rubbed on intake tube. Exposed copper was visibly corroded. Replaced positive cable. Still just a click. No crank.
Replaced starter relay because that was the only thing left in the circuit, other than the negative cable. Still just a click.
Went and bought a new starter motor, which solved the problem. While walking into the store to buy it (same store where I had the old tested originally) I saw a note on the door - "no tests, equipment broken". In fiddling with the old starter, my impression was that it had a bad solenoid and was not a problem with the actual motor.
If you are getting the starter relay click (bolted to side of engine compartment, just rearward from battery) but no noise from starter, then check your voltmeter. If the meter drop a lot while you hold the key in the start position, I'd say replace the whole starter. If not, and you have already replaced the positive cable to the starter, then it just about has to be the starter solenoid, which can be purchased/replaced separately from the motor.
