Jack do this:
1-- Fit good known battery, well charged, reading over 12volts ish
2-- Remove clean and Vaseline all connections for all the -ve wires ie all chassis connections, then do up tight on clean surfaces.
3-- Remove +ve wire on battery and clean, Vaseline, re tighten, the other end should go directly to the starter, remove this connection and clean, Vaseline, re tighten. NOTE do NOT connect any other wires to the Starter connection.
MOST IMPORTANT
Remove fan belt so alternator can not turn, otherwise with its wiring disconnected it could get damaged.
4-- At this stage the only thing connected is the Starter motor, so by pushing the starter peddle on the floor the starter should crank the engine over, it will not start as there should not be any connections to the coil so no spark, so no start....
Try this if successful then move on to another bit, if engine turns over then fit your old battery and try again if it will not turn over you have a duff battery.