91 240sx won't start

[Ben27]

Hi. I'm new to this forum and I'm in need of help. I have a 91 240sx that wont work. I was told it's an OBD1 OBD2 swap with the harness I guess. But don't know how that works. The car will try and start but won't and then all I hear is clicking sounds and I replaced the battery MAF and knock sensor and cap and rotor. But still the same problem. Also checked for vacuum leaks but there aren't any. So if any one can help it'll be greatly appreciated.

[PapaSmurf2k3]

Is it turning over at a reasonable RPM?
If not, take a look at your battery terminals and make sure they aren't corroded. Even with a fresh battery, if there is a lot of resistance through the terminals/cables, the vehicle wont want to start.