So I just got finish replacing the engine in my 07 Scion tC and whenever I try and crank it, it makes the ticking sound but doesn’t start. But when I put the negative jumper cable on a starter bolt it starts right up. I checked my battery with the voltmeter and it’s fine. Only thing I can think of is
the negative cable is messed up somehow? Or I did forget to put the ground wire that’s attached to the wiring harness on. The one that’s in between the intake. Will that stop it from starting because I really don’t want to have to take the intake off after I just put the engine in and everything together.

 

Does your volt meter measure CCA's? If it's clicking it's getting power to the starter, just not enough to use it. I'd try a fresh battery.

 

Wiring is wrong somehow. Applying negative ground-cable to starter anywhere should not cause it to run.

1. Starter is grounded by case bolted to engine/bellhousing. Adding additional ground cable does nothing.
2. There should be ground cable directly from battery -ground terminal directly to body of car. Is it attached?
3. Starter is activated by starter-solenoid transferring +12v from battery +positive terminal to starter's +12v terminal.

Use multimeter to measure following points:

1. voltage at battery's +12v terminal. Volts = ???
2. follow cable from +12v terminal of battery to starter-solenoid's input +12v terminal. Measure voltage at starter-solenoid's +12v terminal. Volts = ???
3. when cranking, measure voltage at starter-solenoid's output +12v terminal. Volts = ???