know how to use a voltmeter? Connect red meter lead to battery cable side of solenoid and black meter lead to starter cable side of solenoid. Should show battery voltage. Now with meter leads still connected, have somebody push the start button. The solenoid should click and the voltage should go to zero, or at least a very low reading. If it does, the solenoid is doing its job and problem lies elsewhere.

If it clicks and does not go to zero, there are several possibilities