Have a 92 Dakota, took part of the dash out to clean the blower motor,
now my Radio won't work, the light on the inside comes on but when you
hook up the antenna or external ground there is a small spark and the
light goes out.

You pinched some wires when you re-assembled the dash. Take apart what you
took apart before, and look for a screw going through a wiring harness.

did you remove the heater control assembly? I did that on mine and damaged
it. Ended up replacing the whole control module and everything worked after
that

You might check to see if any ground wires were reconnected. On my
truck there's a tab on the back of the radio to connect the ground.

Ken