Electric Gremlins. . . grounding problem(s)?

[abeamreach]

I have a 2007 Ram with 6.7 Cummins that has some intermittent electric gremlins. A couple weeks ago, the issues I was having were very occasional but now they happen often. My aftermarket trans temp gauge displays very erratic temps. My aftermarket radio (with GPS) has a hard time tracking on the map (losing GPS connection?) and often changes screens to the backup camera (which is only supposed to come on when in reverse). Neither of these were installed recently. They have been working fine for years. Less often but .. . the air conditioning and power to the electric locks / windows, as well as the aftermarket gauges goes completely out and then cycles on / off erratically. The airbag light comes on when this happens. Finally, on very rare occasions I get a sound like the starter is engaging whilst the motor is running.

I suspect these symptoms all point to a grounding issue. Thoughts? Does anyone have a diagram / picture of the grounding points that I should be checking under the hood?