trans swap question

my question is almost the opposite of what everyone else has done...first off, vehicle is a 2000 xj 2wd...the sun gear crapped out in my buddys xj so he decided to just swap transmissions instead of a rebuild. he got a used unit from a 98 cherokee with harly any miles on it and i went to work swapping. i had to rewire one harness, and swapped over the nss harness (pain in the *** to get it off!) it was at this point that i realized that the trans i pulled had two trans speed sensors, and the one i put in only has 1(rear). also the sensors are slightly bigger in circumference on the 2000 trans. i ended up splicing it and left the front trans speed senson harness attached to the harness and tucked it out of the way.
after about 1/4 mile it threw a check engine light (p0720) for the speed sensor, which i guess you can say i expected. it drives great and has plenty of power, but is there a way to clear up the check engine light? is the trans okay running on one sensor?
i need a little help here... this seems to be the opposite of what everyone else is doing...old into new instead of new into old, haha.