car won't crank.

What does a voltmeter say at battery terminals when cranking? Measurement points such as battery posts, + post to starter relay stud, - post to engine, provide usable information to diagnosis problem.
The battery voltage when cranking should be above 11V. The voltage drop between battery +, and starter relay stud to 0.1 to 0.2V max. Battery - to engine 0.1V, all when cranking.