The electrical system is different than most conversions.  The house battery is not directly connected to the vehicle battery/alternator for charging.  The house battery is always charged with a proper 3 stage charge profile.  House battery is only charged with the shore power charger or the solar panel controller which both charge correctly.  Charging by directly connecting to the vehicle charging system with a ACR relay does not charge the house battery properly.  There are two sources of shore power.  Real shore power or "shore power" from a 1000 watt pure sine Samlex powered by the vehicle 12 volt system.  The 120 volt AC output from the Samlex Model # SA-1000K-112 vehicle powered inverter or shore power can power the house Magnum 3 stage shore power charger.

The shore power connection is just a 3 prong plug hung below the driver's door on an aluminum angle.  Out of sight when not in use.  Out of the weather when connected to an extension cord.  A 15 amp shore power connection is all that is needed for a small conversion if air conditioning is not required. A 3 prong plug is also more convenient for my use because I connect to houses more often than to an RV Park 30 amp receptical.  I do carry a 30 amp to 15 amp adapter.

There are two selector switches in the system.  The first selector switch is used to select either real shore power from the shore power plug or "shore power" from the vehicle powered inverter.  The second selector switch directs the shore power to powering the house 120 volt AC system or the 625 watt shower water heater or the 750 watt baseboard electric air heater.  The 833 watt Magnum 3 stage house battery charger can be run when shore power is available.  The 833 watts is used when the Magnum is set to charge at its maximum 50 amp charge rate.  My Magnum is set to charge at 40 amps or 667 watts.

The single 300 watt solar panel with a MPPT controller is the primary method used for charging the house battery.  The vehicle powered inverter is the backup method of charging if weather conditions force its use.  The backup is seldom required.

If shore power is available, the Magnum inverter/charger/transfer switch automatically transfers the shore power through the inverter to the string of 120 volt AC duplex outlets.  Without shore power the Magnum can be turned on to power the same string of duplex outlets.  The Magnum remote control is used to turn on the charger or the inverter.

The Magnum MMS1012 is a pure sine 1000 watt "house" inverter/charger/transfer switch.  It is a combination inverter/charger/transfer switch in one housing.  Magnum has both the ME-BMK battery monitor and the ME-RC50 remote control.  The remote is used to program the Magnum and is a display to show the "state of charge" of the house battery.  Remote can also display amps in/out, totals and other information.  I could care less what is happening.  I just want to know how much of the battery capacity (SOC) that I have used which gives me the information required to plan electrical use.  The Magnum is only turned on when I need 120 volt power.  Idling the Magnum without loads consumes too much power.

The advantages of the two inverter design are:
1.  House battery is always charged with a correct 3 stage (bulk, absorb, float) charge profile.
2.  The house 12 volt system can be completely separate from the vehicle 12 volt system.  House system can not affect the vehicle electrical system.  House system is not grounded to the chassis.
3.  Not charging directly from the vehicle 12 volt system avoids charging two different batteries at the same time.  Batteries of a different style, size, brand or even manufactured date should not be charged together.
4.  The load on the alternator is limited because the loads are limited.  Either 667 watts for the charger (40 amps charging) or 750 watts for the Sous Vide water heater or 750 watts for the air heater.
5.  120 volt AC power can be available with engine running without using the house inverter/battery.
6.  The refrigerator runs on 120 volt AC power when it is available instead of from the house battery.
7.  Shower water heater can be a simple inexpensive system with a electric heating element and a non pressure tank.  No plumbing or hot/col water mixing required.
8.  Baseboard electric air heater can be powered with the engine running.
9.  Smaller 14/3 AC cord to house system instead of heavy 12 volt DC cables.
 
The disadvantages of the two inverter design are:
1.  Not as efficient as a direct connection to vehicle battery/alternator due to the 12 volt DC to 120 volt AC and then back to 12 volt DC.  That will affect the fuel consumption but probably not by enough to measure.
2.  Costs more than a ACR charge relay.  About the same cost as a B2B charger.
3.  Engine can not be started with the house battery without jumper cables.

The complete wiring diagram for the Transit conversion shows the details of how the system is wired and includes component part numbers.

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Electrical Diagram Drawing # ODJ127-37                                                        

If you want more PDF menu choices the drawing can be saved to your computer and then reopened with Adobe PDF Reader.  The Adobe PDF Reader is a better program to use for viewing.