Check out this schematic. It shows that pin 9 on the TM102 “output” connector is where the device senses the chassis battery voltage. This pin connects directly to the charge bridge via a 1 amp fuse.
So, with your voltmeter connected to a good ground, I would check voltages at the chassis battery terminal of the charge bridge, at both sides of the 1 amp fuse (there’s a test point at the top of the fuse) and at pin 9th of the “output” connector of the TM102.
If you have voltage at pin 9 then it would appear the problem is the TM102, but I would like to think this is the least likely scenario, but we’ve seen the TM102 have issues due to a lack of a flyback diode on the charge bridge.