Help w/ elect. connection. Not on diagram

ECU went out, verified by 2 cos. Checked all parts and for shorts prior to having ecu checked.
Question, came across a w/b wire tied into the w/b that goes from power transistor to the ignition coil. Followed the splice and it goes back to under the dash but no wires as such are listed on the diagram. Any idea why or what would be appreciated.
Thanks

If that looks like a PO's DIY splice, it was probably just a power take-off for some add-on they wanted to receive key-on power, such as an aftermarket stereo amp.