ACX5740 appears normal when powered up but as soon as a card reader is wired, the card reader is continuously in "power up" sequence whether reader voltage is set to 5V or 12V. The reader is designed for either of these voltages.
The ACX5740 power input was miswired at the power supply. It was being powered from the battery charging circuit instead of the DC output of the power supply.
The charging circuit apparently uses a pulsing 24V DC voltage designed to recharge a battery. When powering the ACX (designed to accept 10-28VDC) it looks normal at first. However, the pulsing of the reader power output is not within the card reader input voltage specs.
The ACX5740 power was miswired. It was being powered from the battery charging circuit instead of the DC output of the power supply. Proper wiring to the power supply DC output fixed the issue.