The other day I stopped at home to grab something and when I came back out my car wouldn't start. When I turned the key I heard brief clicking then nothing: no click and no radio, lights, etc. I tried jumping the terminals on the starter and it didn't work. I had a spare new starter lying around and installed it. The same thing happened again when I tried to start the car as before. I cleaned the terminals and got my battery tested, but still no start. After the initial clicks the first time trying to start nothing happens. Any ideas on what it could be?

 

Tested the NSS using the bypass trick and that didn't work either

 

Start simple. Battery connections, how are they? Tight? Clean?

 

Yep. Connectors and cables. Check them first. They may be corroded and presenting a high resistance to current flow. They may allow enough current to light your lights and operate interior accessories, but not enough to make your starter happy.

If you have a meter, do this:

1. Attach the meter's leads to the starter B+ terminal (with all cables connected normally) and to the ground post of your battery, or to the engine block. Make sure you have a good ground.
2. Read voltage. Should be 13.8 or so, if the battery is good.
3. Now, while watching the meter, have an assistant try to start the car.
4. If the voltage drops to zero, or close to it, you have a bad connection, likely corrosion, on the main cable going to the starter. That could be in the cable itself, or in the battery terminal, or anywhere on that circuit.

If you do not have a meter, get one. Even a $10 Harbor Freight model is fine. You need SOMETHING to measure voltage.