GA flight student with instructor reported the aircraft navigation and communication equipment malfunctioned during final approach. It was discovered post-flight that a loose piece of aluminum tape in the engine compartment had caused an electrical short.

Narrative

During an instrument training flight from ZZZ1; I was flying my first approach of the trip under simulated instrument conditions with my CFII as acting PIC. We were flying the ILS XX into ZZZ and were on an active IFR flight plan with ZZZ Approach. Our route for the day was mostly VMC with some stretches of IMC as we flew through a line of light precipitation on our first leg. The flight until this approach was standard; no indications of any equipment issues. Our C172 was equipped with Dual Garmin G5s; a Garmin GTN 650 and a Backup Nav/Com. On final approach; I estimate around 100 ft over minimums; I notice that the glideslope and Localizer indications begin to flicker on and off. I glance at the GPS and Radio and they are all flickering; as if their power is being cut and then reapplied every half second or so. Since we were in VMC; my instructor and I decided to land full stop at ZZZ to investigate the issue instead of returning to the air with a clear electrical fault. We tried to contact approach on the ground via radio but found that our radios all shut off when he press the push to talk. We canceled our IFR via phone when we cleared the Runway. We parked at the FBO; shutdown; refueled; and tried to troubleshoot the issue. Unable to get the plane to start; we found a mechanic on the field who agreed to help us figure out the issue. He removed the cowling; investigated and discovered a piece of Aluminum Tape that had fallen off somewhere else and bridged a battery terminal and the airframe. It appeared that this same tape was used to patch over cracks in various places under the cowling and around the engine assembly; and it could have fallen from many places. Our battery was drained to 17V (nominal is 24V). The mechanic helped us jumpstart the plane with an external battery and found that our alternator was also only outputting 23.5 V (Nominal should be closer to 27V). Knowing that our alternator was not outputting enough to charge the battery properly; and the presence of potential IMC between ZZZ1 and ZZZ; we decided to remain at ZZZ and have another pilot come and pick us up in a separate aircraft. Since we were in VMC at the time of the failure; there was no major safety risk to us however if this had happened 30 mins prior when we were in IMC; then this would have quickly turned into a serious emergency.