The car inverter is likely square wave output which may not work for the mount.
The mount runs on DC and doesn't care what waveform the AC is, square wave or sine makes no difference because it doesn't appear on the DC side.
From: Steven Panish <scpanish@...>
To: main <firstname.lastname@example.org>
Sent: Sat, Feb 1, 2020 6:41 pm
Subject: Re: [ap-gto] Inverter issue
Don is correct, although typically if you pull too much current out of an inverter it will blow a fuse or breaker. Try running the mount right off the battery if you can make up a cable. Fusing that is a good safety precaution. It is also possible the the AC to DC converter has a bad connection which is showing up in the field.
The car inverter is likely square wave output which may not work for the mount. And BTW, if the main inverter is failing and putting out a poor waveform, some devices will work, and some will not.