Electrical Problem

As you stated, you have an open ground. It's that simple. The voltages you are reading are due to the capacitive coupling to other nearby wires. I will guess the ground isn't interrupted near the socket you are measuring, but further away thereby giving the ground wire you are measuring a chance to run in parallel with other wires for a ways. If you were to put any kind of load across either the 70 or the 50 volts, the voltage would drop to near zero because it isn't really connected. Modern volt meters are designed to load the circuit very lightly because you might be measuring sensitive electronics. In this case, you would want a load to avoid the phantom readings you are seeing.

Hi, Are you using a DVM, not something like Simpson 260?

Hi, Load as a small light Wattage bulb.

If you truly had 125V from hot to neutral, what ever you were testing should be working.

Why are you testing for an open ground?

Find every outlet on that circuit by turning the power off and start opening all the boxes on that circuit.

Analog

I found every circuit by using a circuit locator. This is in a trailer and the boxes are sealed, that is, the outlet IS the box clamped shut over the wire. Total pieces of junk.

If only one receptacle shows open ground, the open could be in that box or the next one nearest the panel. It may not be in either box, but those two are good places to start.

Fix the open ground, and don't get too worried about the trace phantom voltages. You can drive your self crazy trying to trace a milivolt here or there.