Taking the switch out was a good idea and isolating everything. As you would think the two loads won’t have anything on them cable 2 and 3. You should measure 120 v from black to white and from black to ground on cable 1. The black wire is the hot wire and the common is white. You shouldn’t be getting voltage readings of anything except zero and 120 so these 20 and 70 volt readings are not right.
What type of meter are you using and on what setting on the meter?
If those readings are correct you have to chase the problem back down that cable to where it comes from. If you have anything you can use as a test load like a light bulb and do it safely you could test at each set of wires and see what the bulb does. If you have the low voltage you say you will see a very dim light at the low voltage. I keep a refrigerator socket with a rough service bulb in my meter box with a set of test leads attached and it’s quite handy for stuff like this.
Likewise I have a power lead that’s fused that I can plug into a good circuit and power up something like your fan cable just to make sure those cables are working the way they should.
From his last post he said he had 3 cables coming into the box number 1 was the power for the circuit and 2&3 were loads one being a fan of some kind and the other an outlet box or something like that. If you remove the switch I was saying the feed into the box cable one would have power to it. It sounded like the power then went straight to the outlet and thru a switch to the fan. That was my take on it anyway. Taking the switch out should leave everything down stream dead.
The other method would be having the power originate at the device and then come to the box to be switched it didn’t fit his scenario as well I thought.
He didn’t mention odd voltages around the rest of the house. Or things not working just this one circuit. Strange voltages make me thing of a missing ground also. Maybe I totally misread his problem I will have to go back and read it from the beginning. I started where he said don’t pay any attention to all the above.