I think you understand this, but let me emphasize it. Your setup, with the Motorola alternator, or any alternator with a built-in regulator, does NOT allow you to connect wires to the alternator field. There are no terminals for you to connect to the field winding. That is because the alternator’s internal regulator connects there internally. So, don’t even think about connecting from the battery to the alternator field via a switch, or anything else.
Blue Sea Systems catalog (
http://pod.delzer.com/powerproducts/bss_cat/) has a lot of useful information on their products, and some simple illustrations with cute drawings.
For example, pg 32 shows some of their manual battery switches. One of these is probably what your “sketch” calls “Sel Sw”. When properly wired, it allows you to select which battery, #1 or #2, is connected to the house/engine loads and alternator (like the 6008), or OFF. Roadnsky’s post shows such a setup.
Your switch may have a ”Both”, or “1&2”, position (6007), allowing both batteries to be connected together. This, from your description, appears to be what you’re aiming for.
All these are manual switches, and are generally used to switch between two similar batteries on a daily rotation, to give equal usage and charge.
If you connect the 3 wires going to the “Volt Div” together, the alternator output will always go to both batteries. While that will work, you won’t be able to disconnect the alternator and house loads from the batteries when in the OFF position. This is a safety thing - in event of a fire or emergency, you’d like to put the switch in the OFF position and disconnect everything from the batteries and alternator. The alternator output and the house loads should be connected to the selector switch’s COMMON terminal (which may or may not be the unnumbered terminal in your sketch), as shown on pg 32.
On Pg 40, Automatic Charging Relay (ACR) and Isolators, is shown how an ACR is connected to do this switching automatically, and how an Isolator is hooked up. From your sketch, you appear to have an Isolator (dead or alive).
The catalog appendix on pg 160, Battery Management Schematics for Typical Applications, shows some common connections with an ACR. Yours may be the one labeled “2 Battery - 1 Engine”. (As part of a marketing philosophy of “don’t confuse the customer, he’ll buy more”, they don’t show an alternator. Instead you get an engine).