Either the probes didn't get a good contact or the red grounding wire has a lot of resistance in it.
It's an either or. You car with the standard transmission has a switch on the clutch or the shifter.
This is from '71 FSM. '72 might still be this style diagram?
View attachment 1715580944
S4 18 ga Dark Green is for cars with Manual transmission.
S4 18 Br/Y* is for cars with an automatic transmission.
The clutch start switch is the ground. When the clutch is depressed, the switch is closed and electricity can flow to ground.
Well then the battery terminal shouldn't be connected to anything, right?
You could recheck it, but that seems to be a problem.
Take off the wires and recheck. If it passes then, the short is in the wiring not the relay.
If it is no good, feel free to open it up so you can see how it works and maybe even what's wrong.
A new one or a good used one should be easy to obtain.