So my s13 won't start (or crank).. I tested the battery cable to the starter with a multimeter and got a good reading of 12.4v.. but when I tested the signal wire I got 0.01v

What is my next step? Do I need to change a relay or harness or something or do I just get a new starter?

You could check the amp draw when sitting there and compare that to the amp draw when trying to start the engine. I'm not sure how you tested the signal wire voltage. Just on the car or was someone turning the key to start for you while you tested? You might try to see if the starter solenoid is moving when the key is twisted or not. When my starter finally went bad, it was because the contacts in the motor had finally worn away. Starts were tougher and tougher until it just wouldn't start anymore.

centralcoaster33 wrote:You could check the amp draw when sitting there and compare that to the amp draw when trying to start the engine. I'm not sure how you tested the signal wire voltage. Just on the car or was someone turning the key to start for you while you tested? You might try to see if the starter solenoid is moving when the key is twisted or not. When my starter finally went bad, it was because the contacts in the motor had finally worn away. Starts were tougher and tougher until it just wouldn't start anymore.

I had somebody inside trying to start the car and the signal wire would go from 0.00 to 0.01 when the key got to the second position

Okay, well check the ground on your engine block in the back by the last exhaust manifold bolts. For relays, you can swap a similar, known working relay from another spot in and that would help with diagnosing (if one works and the other doesn't, you need a new relay).

Ooh, found this juicy thread, check it:
1991-1994-240sx-starter-not-turning-eng ... 49966.html