It was stated above that amps are needed to turn the starter motor. This is certainly true. But volts are needed to provide the force to push the amps through the starter motor. If the battery is bad, as soon as you try to use the starter, the battery voltage will drop and the voltage will not be high enough to provide the amount of amps that the starter motor needs.
One can spend a lot of time checking, cleaning and reattaching connections in the circuit. But it can be more efficient using a voltmeter and determining where the actual problem is. The first and most simple check is the put the voltmeter leads on the battery terminals themselves, not the cable clamps, but the actual battery posts, and to try to start the tractor while monitoring the battery voltage itself. If battery voltage drops significantly low at the time the starter is supposed to be engaged, there’s no need to look further. The battery is defective.
If the battery voltage does not drop and stays at 12 volts or so, then it’s time to make other measurements at different points in the circuit and isolate the problem wherever it may be. The next step might be to measure the voltage at the starter motor. When the tractor ignition switch is put into the start mode, if the voltage at the starter motor drops low, when you know the voltage in the battery did not drop low, then you have a bad connection/cable someplace between the starter motor terminal and the battery. Keep in mind that if the battery voltage stays high at the starter you could still have a bad connection in the return side, which is mainly the connection between the engine and the tractor frame probably. Measuring voltage between the starter motor case and the negative battery terminal would confirm this. It should always be very close to zero.
You can actually find the bad connection by measuring voltage between points in the wiring between the battery terminals and the starter. For example, if you put one voltmeter lead on the battery post and the other voltmeter lead on the clamp that is connected to the battery post, you should not read any voltage when you try to start the tractor (depending on how good your meter is it might display some voltage but it will be very low). If you read voltage the connection between the clamp and the battery post is poor. The same approach can be taken anywhere along the circuit both on the Positive side and the negative side. By doing this you can save a lot of time isolating the problem by not having to take apart, clean, and reassemble every terminal/connection in the circuit.
