Ammeter to Voltmeter...who does it?

Mattax said
Yes. If you run a charging wire to either the solenoid, the relay or battery post, all power for charging will be diverted from the bulkhead connection and dashboard ammeter. You may still see some flow on the ammeter during start, because that might be be the shortest path from battery to ignition switch. 5 amps at most, less if some goes the other way.

Good to know I can follow what you guys have been saying and learn from it.

Mattax said
It could be the insulation - in the photo the alternator output wire bulkhead to looked heavier than the battery feed.

You could very well be correct. The Service Manual is very sporadic about the MB300 chassis cab...it was primarily written for the regular B-vans. Since it makes no mention of the 100A voltage regulator that's in my rig, it stands to reason that the wiring might be a bit more heavy duty as well, which means that the wiring schematic isn't complete for my model.

Mattax said
My question about the regulated power supply for coach was for calculated current loads. I don't know about a fridge. For lights, if a bulb is rated at 12.8 Volts and is given power at 14.2 Volts, more current will flow through it. So if adding upo current loads, something to keep in mind.

At 12V, the Dometic RM66 fridge ammonia heater uses 11A; the 110V side uses only 1.4A.

Mattax said
This circles back to your question about the alternator and whether the original blue tag one will do the job. And yes, once the direct charging wire is added, the my question is whether the 60 amp has an advantage because it is self limiting. In other words the recharging rate will be 50 amps or less even driving on the highway. Lets assume 55 amps at 14.2 V, less whatever starter battery needs to get recharged, less equipment needs (5 amps for field and ignition minimum).

Now lets say a '100 amp' alternator can put out out 90 amps at 14.2 Volts while driving 35 mph or faster. That would let the coach batteries draw as mcuh 85 amps when they start to recharge (assuming they were very drained).
Might see what battery manufacturers recommend. These may be deep cycle batteries which might be OK with it. This isn't that different of a situation than boats with cabins, or airstream and other rvs.

The Interstate Battery guys near me are pretty savvy about what deep cycle batteries need. I'll talk to them, as well as the alternator rebuild shop down the road. I found this diagram in my Dometic refrigerator manual. Adding a relay sounds like a great idea.