Try this

Hook the red alligator to battery pos, blk to neg battery, and the test lead to the #3 pin on the DM connector box
Key ON . press button for 2/3 sec , release and see if codes come back.
What we are doing here is powering the tool direct with Battery 12v, as to eliminate any wire/fuse problems [ or sw/led ] the DM connector is having

I am assuming you have tested y6our new tool for correct led polarity???????????