Dave
First welcome to the forum, A Little information about what were working on is always helpful.
I am not sure what your mechanical abilities are, but Simple diagnostics goes along way. It is easy to test the starting and charging systems, but there are some things that you will need. DVM and an extra set of hands.
I am not going to take the time to list all the testing as of yet.
First test you need to do is a Battery test, when I say Battery test I do not mean to see if the head lights come on. Instead you need to find out what condition the battery is. It can be done with a DVM.
1. Connect the Positive lead from the multi meter to the Positive POST of the Battery NOT the Positive cable.
2. Then connect the Negative lead of the multimeter to the Negative POST of the battery NOT the negative CABLE.
3. Observe the meters reading's you should have 12.6 volts on a fully charged battery.
4. Next with the multi meter still attached to the battery POSTS, have an assistant crank the engine, Observe the reading on the multi meter, It should be at LEAST 9.5 volts. Any less then 9.5 volts and the battery needs to be recharged then tested again.
Now if the battery tests described above all check good then it is time to do a voltage drop test on the starting system. To do the voltage drop test you will need
you multi meter and an assistant again.
1. Connect your positive lead to the POST on the starter motor.
2. Then connect your Negative Lead to the Starter motor POST from the solenoid.
3. Have your helper crank the engine, Your meter should read NO MORE then 0.5-0.7 Volts.
If you get a reading Higher then 0.7 then you have a resistance in the circuit, which is a loose, or corroded connection in your Positive Battery cable between the battery and the starter motor.
4. Connect your Positive lead to the NEGATIVE battery POST.
5. Then connect your Negative lead to a clean unpainted surface on the starter motor itself.
6. Have your helper crank the engine, Your meter should read NO MORE then 0.2-0.3 Volts.
If your reading on the Negative side Higher then the 0.3 volts you have a restinance on the Ground side of the Circuit, which would either be a loose or corroded Ground cable from the battery to the engine block itself.
Another test that needs to be done and should actually be done before the voltage drop testing is a source voltage test at the solenoid. To do this test you will need a multi meter and a helper again.
1. Connect your multi meter Positive lead to the Solenoid POST labeled (S).
2. Connect your Negative lead to a clean unpainted surface of the starter solenoid.
3. Have your helper crank the engine.
4. You should have battery a voltage reading equal to the voltage of your battery.
If you don't, have any voltage then you need to check the neutral safety switch.