Cessna 172 technician reported during troubleshooting of the aircraft electrical system; found connectors installed were incorrect type. They installed new connectors but installed them incorrectly.

Narrative

Customer found that the ammeter in the aircraft was erratic and bounced back and forth when running. Inspected and troubleshot defects to the voltage regulator. Upon further inspection found connectors installed were incorrect and require Molex connectors. Installed on aircraft side new Molex connector and crimped wires. Completed install and ops checked aircraft. All ops checks passed at time of test.Aircraft had training flight that took it to ZZZ; I was informed after takeoff returning back to ZZZ1 that the PIC encountered radio loss along various other electrical issues. Assistance was requested and the aircraft returned safely back to ZZZ.The onsite mechanic found that the new wires that were crimped on were incorrectly fashioned.I am aware of the mistake and know now what caused the inadvertent emergency landing of the aircraft. My judgment on placement of the wires in reference to the pin crimp location was incorrect and I have taken the time to refresh and retrain on proper crimping when using the Molex application.