Just replaced the alternator and starter and battery reads at 12.5 volts but when I try to start it, the engine will turn over once and the starter will start clicking. Bad battery? Anything I should look for? Also tried using a battery charger and jumper, still did the same.
Check and clean the ground side connectors: battery to ground, engine to ground. When you get a click that means there is a voltage drop somewhere. First measure the battery voltage while it is clicking. If good, then measure voltage between battery negative post and engine block. For example, at the alternator bracket. As a final check measure voltage between the large starter terminal and the negative terminal. That missing voltage is somewhere in the loop.