Must be 100s of threads on the "click when I turn key to Start, but no crank" problem. Search for "yellow wire".
- Sounds like the battery is probably fine - but get it load-tested anyway to eliminate it.
- Solenoid gummed up/not throwing out. Hitting it with a hammer might free it.
- Dead/burnt spot internally in starter. Rebuild/replace.
- Bad ground(s) - especially transmission ground strap. Clean, check, fix.
- Poor battery connection(s). Clean, check, fix.
Those are the easy ones. The starter itself is permanently hot, bolted to a big fat cable. Clean/check this by all means - but I don't recall anyone ever reporting that to be the problem.
Starter cranking is controlled by the infamous yellow wire on the solenoid terminal - which must deliver plenty of voltage and current both - or the solenoid will only click, not throw out to engage the starter.
You cannot test this with a resistance meter or a test light - it requires not only voltage (significant voltage drop at the yellow wire is a huge red flag), but also to pass a healthy amount of current to throw the solenoid arm out (DC clamp ammeters are cheap).
Electrical path to the solenoid terminal, left alone for decades, doesn't tend to improve. With an ageing solenoid, requirements for voltage/current only tends to increase as the grease hardens. So at some point operation can become "marginal", if it doesn't fail altogether (which, whilst inconvenient at the time, is actually your "best case" scenario for diagnosis).
There can be a problem with the yellow wire current path anywhere from the
- feed from the battery to the ignition switch
- start pole in the ignition switch itself
- ignition switch connector to harness plug
- 14-pin connector in the engine bay that the yellow wire runs through
- ground connection the the current needs to return through for the solenoid to work.
You may need to clean/spread harness connectors undisturbed for many years. These can gradually deteriorate as the connectors oxidize...
If it's an intermittent fault, it can be hard to pin-point - because you don't know if it's actually fixed, only that it hasn't happened again...
Mine would refuse to crank when it was cold/damp - only to work perfectly 2 hours later once ambient temps had come up. Even flat-bedded it to my wrench once - naturally, started on the key when it got there. So the next time it refused to crank on the driveway one cold morning, I fixed it myself (was dirty connectors in the 14-pin plug)...