I am not the right person to answer because my AMP always works well, but considering you are waiting for a response, here is my contribution based on Papajam diagram:
Be sure your #6 fuse on fusebox B is ok and then check if you have +12V to ground in both AMP meter terminals with the ignition switch in start. If you have voltage in both terminals your meter is ok. If you have voltage in the black and nothing in the red, meter coil is open. Disconnecting both wires and with a continuity test you can doublecheck the open condition. Meter coil can be rewired but you need to check the overcurrent source that causes the coil to open before fuse #6 opens. If you have nothing in both wires, you will need to check your black wire all the way down to the starter and ignition switch, including the +battery connection. I will not adopt the old school method of short circuit the AMP meter terminals with a screwdriver to see what happens because it could damage something else.