Car wont turn over after swap!

[btwilson86]

OP, you said that you replaced the big wire that goes to the starter (i'm assuming that this is the one that you said only had 400mv); what is the voltage at the wire now? This wire, at all times (regardless of if the key is on, clutch is pressed, alarm is armed), should always read the same voltage of the battery. Period. It is a direct connection to the battery, there is nothing inline that can cut the power to it.

Do this in the order listed below:

1. You said it's a new battery, have you verified that it still has a charge? Use your volt meter and check the voltage of the battery between the positive and negative posts. If this isn't around 12 volts, charge the battery.
2. Check the voltage of the big wire at the starter to the negative post. If this is not the same as #1, inspect the positive battery terminal. If it is, continue to #3
3. Check the voltage of the big wire at the starter to a clean spot on the engine block. Voltage here should still be the same as the above two bullets. If it is not, inspect your negative battery cable for damage, corrosion, or poor connection at each end.

If your voltage is still the same, then your problem lies in the circuit leading to the small wire on the starter, or within the starter itself. As Travis89Turbo said, just because it's new doesn't mean it's good. All parts have a percentage of defects out the box, yours could be one of them.