From your description, it is clear that the PCM is in self-test mode (STM). I will assume that you didn't leave a jumper installed in the self-test plug.
To enter STM, the Self Test Input (STI) lead (that's the small, single wire plug) is connected to the Signal Return line in the EEC Test connector. Connecting this signal line to chassis ground will produce the same effect.
I'd suspect either your STI signal is shorted to ground or your PCM is internally defective.
With power off, check the STI lead for a short to ground or low resistance. If it is low or shorted, unplug the PCM and retest to see if the short is in the harness or the PCM.
Inspect your wiring harnes for bad insulation.
Steve
