I had problems with the positaps I found on amazon. Went to my local car stereo installer who gave me some great 'snap on splicers' that when I searched on line I could not find anywhere. Worked like a charm. Another friend said that he removed about an inch of the insulation from the wire he wanted to tap into, parted the wires to make a 'hole' in the wires, threaded about 1/2 of exposed wire that leads to the 'T', pushed it thru the 'hole' in the original 'hot wire', soldered it, and insulated the whole splice with liquid electrical tape.
I did not want to do the latter just in case I wanted to remove the lighted T in the future.