One of the main hazards of working on or in your Sprinter has to do with its electrical system. Some of the info that follows is also found in the vehicle manufacturers manual. Especially the procedure of disconnecting the main vehicle power.
To do your build you must understand this main battery disconnect (which is actually the main “Chassis Ground” disconnect from the battery under the floor of the drivers feet. Perhaps multiple batteries in some configurations?
Then understand how you will wire up the “house” side of your electrical system. Will you use chassis ground as you preferred configuration on the “house” side? That may be more complex and unwise than you realize.
I personally installed isolation switches between my vehicle chassis battery and my “house” system. Then wired out my entire “House” system with 2 conductors to every “house” load device. Not using any chassis grounds on the “house ” side. This includes 3 alternate charging sources. A 110VAC to 12VDC Park power converter – charger, a Battery to Battery charger, and a Solar Controller – Charger.
Many build systems that are isolated or incorporate a means of disconnecting the “house” side of things that might tap off the vehicle for some secondary source of power or “charging” capability. Especially at times your vehicle may be in for service and a mechanic needs to disconnect ALL power. They will only know about the Mercedes main power disconnect. Think of your service person too. They will have no clue how you wired anything. I am sure they will not be responsible if something electrical gets trashed because there is still power to things after they might disconnect the main Mercedes disconnect?
The manufacturers manual/book info is somewhat helpful for finding the disconnect, and how to do a disconnect. That is, if you are the type that actually reads the entire manual, understand it in detail, then actually retain all that info. The manual is lengthy! Plus many may be buying a used vehicle and never end up with a manual in the first place.
Even with this knowledge, DIY wiring can easily disable the factory disconnect feature. You may back feed from auxiliary batteries if you used chassis ground for anything.
I am sure the newer the year you are dealing with, the more this warning pertains. The electrical systems, computer, and sensors are very sensitive. Should you start messing around with power applied and unplug a connector, and even properly reconnect it. You have a very high chance of triggering a sensor that may generate a fault/error code to the computer. This error code may turn on a warning light. It may also be the type of error code that must be cleared by the dealer. Some error codes won’t go away no matter how long you drive the vehicle, or whether you do a main power disconnect after the fact. (The seat belt and air bag sensors/lights are known for this)
If you think you are going to run out and buy a inexpensive handheld device to reset codes on the Sprinter computer, think again. Especially if your Sprinter is only a year or two old. Most of the manufactures of these devices lag about 2 years behind developing the software to be compatible with Mercedes Sprinters. So even resetting a Seat Belt or Air Bag sensor may not be possible as a DIY. It will mean a trip to your dealer, and sometimes a charge to do it.
There is a wide variety of factory and non-factory battery configurations. Some basic systems have just 1 battery. In most cases, that is the battery located beneath a floor panel at the drivers feet. Others have additional auxiliary batteries. Some found in the engine compartment, under the passengers seat, and various other locations.
One of the oddest and quirky things you might run into is the tiny computer back-up battery that is located under the drivers seat. Its a small lithium brick. At least I know its in the 2019’s. This is to prevent loss of computer programming should you leave the “main power disconnect”, disconnected for some long period. But as time goes on, this back-up battery could become defective?
The point being, if you disconnect the main power you should not return the computer to default settings. But if this back-up battery is not holding its charge, and you open up the main power disconnect, you may have to reset anything you have custom altered via instrument panel/steering wheel controls, including the radio.
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