Originally Posted by steve(ill)

dont ever pull the positive cable off a battery when running with an alternator. the alternator charges 13.7 volts because it has feedback from the battery. without the connection it will hopefully die. it is possible for it to jump to 20 volts and blow out the computer and all lights, etc.-- dont ever remove the cable from a running truck.

Originally Posted by LxMan1

Yep, if the PCM lived, you're lucky. The battery acts as a capacitor that absorbs any voltage spikes. I have seen where someone did this on an older vehicle and blew all of the light bulbs out of the car because the alternator was overcharging.
You may be lucky because your alt. isn't charging.