What causes the battery light to come on along with the ABS light

After driving the car for about ten minutes, the battery light comes on along with the ABS light. Also, the RPM gauge turned backwards and now the needle is stuck behind the little peg the needle usually rests against (when the engine is turned off)only this time it tries to turn clock wise but the peg holds it back. The mechanic checked the alternator while the engine was running and the battery light was on and said the alternator was charging. By the way, it's a new alternator and it's making a funny noise. He placed the leads at the battery posts, how can you tell if the voltage being read is from the battery or the alternator?