My car will not start and I have replaced the entire starting system in my 1978 ford ranchero. whats wrong?

With the information you provided I would start looking at the wiring and ignition switch circuit to deal with the no- crank at the ignition problem. The second situation with crank but no start except with a jump box would make me turn to the distributor and cap/rotor and spark plug wires. Inspect these components and see if you get spark. Good luck.

you left out the battery. have it checked out.

Mileage since Rebuild........or Mileage? is Engine Relatively easy to turn over by hand? Have the Battery Fully Charged then "Load Tested" at 50% of CCA (Cold Cranking Amps) for 15 Seconds not dropping below 9.2 Volts during the test to see if the Battery will Take & Hold a Charge. "Does the Engine make any scraping sounds? or Metal in the Oil Pan?" {First is Maybe Bad Battery, Second is a Possible Rebuild} at 33 Years

Double check the main ground cable connection at the engine block.It appears that the large electrical current cannot flow from the starter back to the battery.

You should have started with the battery, well at least you now have a couple hundred bucks of new parts on your "classic" and a new battery will make it crank over great.

If you jump the battery and it turns over, then you just eliminated the cables and starter out of the equation. You never mentioned the battery at this point. Check the battery by fully charging it and preform a load test on it, you may have a bad cell. Now did the engine start when you jumped it? This is another question for you to ask once you replace the battery and get ignition. Remember, you need fuel, compression and spark to start the engine. Make sure you have all 3. You may have a bad timing chain if no compression. good luck.......

Do you check if it turns if you use wrench on the crankshaft bolt in front of the engine. I'm afraid your engine is stack or timing belt is gone!