Thor Chateau 2020 not charging coach battery from alternator

[steveb48@aol.com]

Hi all,
This is actually my neighbor's RV. Coach lights and accessories work. Shore power and generator charge the battery. Alternator does not. Found the isolation contactor under the hood below the coolant tank on the drivers side. 2 large red wires, one to the main battery and one disappears below the rig, I assume to the coach batteries. Measure the voltage from each terminal to ground, 12v (ish) on one, zero on the other terminal. Start the engine, contractor goes click and now we see 13v (ish) on both terminals. Is there something (fuse, breaker) between that contractor and the coach batteries? If so, where? I looked all over and couldn't find it. I have another friend with a Jayco and has the same problem.

Thanks,
Steve

[CHS]

I have the 2019 (2018 chassis). Disregard the (Sprinter Chassis) fuse block. Unless they updated the system in the 2 years, all else should be the same.
If you have 12 (ISH) power on one leg, you may have a loose and/or bad wire or connections somewhere.

[steveb48@aol.com]

Thanks for the schematic. It looks close to what we saw yesterday. I saw the 70 amp breaker. I'm surprised that there would be no fuse / breaker between the 2 sets of batteries. If this is the case, it's just a wire between the contactor and the coach battery. Everything I can see is tight. I didn't look for a crimp on the insulation. That would surprise me but...

thanks again,
Steve

[Pillbox]

Try this schematic.