You used a DVM? 80V sounds a lot like phantom voltage, induced by nearby wires. It's a bit like how a crystal AM radio can use the radio waves itself to power a tiny earpiece. This can be picked up by very sensitive digital meters (as contrasted with an analog meter where the voltage must have enough motive force to move the needle). It is not real, usable voltage, and actually means the wire is disconnected.
The easy way to test for phantom voltage is use a less sensitive meter, or put a tiny load on the circuit. The tiny load will quickly extinguish the phantom voltage.
- Shut off breakers (until the voltage indication is gone) and attach the two wires to a receptacle, or
- just screw in a light bulb socket adapter...
... plug in an incandescent night-light with a switch. If the voltage disappears when you switch the night-light on, that was phantom voltage. Treat it the same as you would a 0 volt reading.
Of course, then you'll need to chase the problem as normal. The good news is, barring nails driven through Romex, 99% of wiring trouble is at the terminations, and Code requires every termination (with rare exception) be inside a junction box which is accessible without deconstructing the building.
It goes without saying that you treat every gun as loa--- I mean every circuit as hot, even when you personally cut the breaker you are sure it is. Things like MWBCs can boomerang back on you.
Once I overhauled the wiring in a factory. The 480V feeder to the buses, and the service entrance wire off the 120V transformers had been stolen. The 1000A 480 service and 480-120 transformer supply knife switches were off. This was way beyond LO/TO, the service wires were gone. I still treated every wire like it was live. You don't want to wire your brain to ever think it's OK to touch copper. This is one reason I pigtail receptacles at a bench instead of hooking them onto screws at the box.