With Pyramids, if the P/S gets overloaded - e.g. short circuit in the cigarette lighter plug, or the screw-on terminals touching each other when tightened – the supply will shut down its output for something like 7 minutes after the fault signal is recognized. It won’t be obvious looking at the mount itself, which appears to still be up & running. This is a safety factor.
I assume the Mach1 uses Power-Pole connectors, or else, if the cigarette lighter plug is used, I have had a case where one of the power leads “inside the plug” had disconnected from its solder/crimp joint.
Also, check the fuse in the screw-on tip of that kind of plug – which would also lose power to the mount, even if the Pyramid is fine.
Check the cable to the mount, and others that the supply may be feeding, in case something else is overloading it. Best to remove any other devices, and simply first test the mount operation alone.