Set your voltmeter on DC voltage (it should have several settings) Be sure it's set on a higher setting than you're testing ... i.e. ... 36V/48V. If you have a setting for 60V - DC, use that one. Place the positive (+) lead on one of the large terminals and the negative (-) lead on the other big post. (If you have them reversed, it should give you a negative reading ... i.e. ... - 38.0V ... that's just a number I'm using for an example) If so, reverse the leads.
Be sure and jack up the rear of the cart, so it doesn't try to take off on you!!!
With the leads in place, slowly push the accelerator pedal and watch the voltage. It should be the same as your total battery pack voltage. If your solenoids are stacked, the top one should be your slowest speed, the bottom one, your highest speed. As you push the accelerator, the 1st one should click or engage, then the next, and so on.
Using the same setting on your voltmeter, you can check your batteries.
Put your positive (+) lead on the (+) post and your negative (-) lead on the (-) post, of each battery. Write your settings down. You can test the whole battery pack by placing the (+) lead on the (+) post of the 1st battery and the negative (-) lead on the (-) post of the last battery. (The cart should be off for this test)
I hope that's a clear explanation, if not ask.