SPRINTER Electrical System Precautions

One of the main hazards of working on or in your Sprinter has to do with its own factory electrical system, and its on board computer module. Some of the info that follows is also found in the vehicle manufacturers manual. Especially the procedure of disconnecting the main vehicle power.

You can create error codes and such by simply unplugging a connector out of proper sequence.  Things you might otherwise be used to doing, and getting away with, while working on other manufacturers vehicles.

To do your build, you must understand the Sprinters main battery disconnect (which is actually the main “Chassis Ground”.  A disconnect from the battery under the floor of the drivers feet.  Though it is actually found up under the dash to the side of the gas pedal.

There are multiple factory batteries in some configurations?  Know what you are dealing with.

Then understand how you will wire up the “House” side of your electrical build-out system. Will you use chassis ground as your preferred configuration on the “house” side? That may be more complex and unwise than you realize.

I personally install isolation switches (DC Circuit Breakers that can be manually popped open when needed)  between my vehicle chassis battery, and my “house” system.  On both the (+) Positive and (-) Negative “Links” between the “House” and “Chassis” electrical systems.

I also use such DC Breakers between various charging systems for isolation and easy fault troubleshooting.  But that is detail that we won’t get into here. Look for links or our website’s Menu indexes for more specific information.  It is updates as we have time.

Additionally I wire out my entire 12VDC “House” system with 2 conductors to every “house” load device. Not using any chassis grounds on the “house ” side.

I have “Main” high amperage cut-off switches on both my (+) Positive and (-) Negative side of my “House” System.  These can be accessed quickly and easily.

My  “House” system includes 3 alternate charging sources.
Battery to Battery charger (B2B) off my vehicles charging system
110VAC to 12VDC Park Power converter – charger

Solar Controller – Charger.

More details on the 3 Charging Source System with a diagram

These three charging sources, are typical “Must Have” charging sources for the RV type traveler.  Those that boondock, use RV Parks with Power, Run off a generator at times.  Or those that simply travel and want all the convinces without messing around.

“House” Battery banks, charger amperage output configurations, and types of both batteries and charger output (Flooded, AGM, Lithium). Those choices will vary wildly from person to person.  Much will depend on your power needs/usage, the “convenience” devices or loads your build, intended duration when “off-grid”, even where you live/camp/season.   Most importantly perhaps…..the size of your wallet!

All of which will dictate what you have to include as part of your build-out electrical system.  How much space it will use.  Where to locate components to reduce costs while increasing power efficiencies.  All of which becomes important to those wishing to run off batteries extended periods of time.

Many build systems  that are “isolated” or incorporate a means of disconnecting the “house” side of things, from the Chassis electrical system.

We are talking about a system is “tapped off” the vehicles electrical.  For some secondary source of power or “charging” capability.  Most want this capability.  But you also need the ability to easily and quickly completely disconnect the “House system” from the “vehicles electrical system”.   It’s truly the wise way to design and build.

This is especially important 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 vehicle mechanic which might ultimately equate to expenses to you in the future. They will have no clue how you or an outfitter wired anything.  They will not be responsible.  Not responsible in the case something electrical, having to do with the factory chassis system, gets trashed because there is still power to things….. after the mechanic disconnects the main Mercedes Sprinter disconnect.  They may even refuse to work on the vehicle end of things?

If a mechanic is troubleshooting a vehicle problem, your “House” system may run them around and give them false faults to eliminate.  You may pay for that confusion as billable labor.

The Sprinter manufacturers manual/book info is somewhat helpful for finding the Sprinters main 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 or display message. 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.  At least cheaply, or for free.  It may mean a trip to your dealer, and sometimes a charge to clear 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 factory configurations have additional auxiliary batteries. Some found in the engine compartment, under the passengers seat, and various other locations.

One of the oddest and most quirky things you might run into is the tiny computer back-up battery.  A small Lithium brick, that is located under the drivers seat.  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.

As time goes on, this back-up battery could become defective too.  So if you disconnect the main, it is conceivable you might have a loss of computer memory, and need that re-down loaded, flashed, or you to manually reset any of your custom settings you may have manually set up through the steering wheel buttons, or display buttons.

The point of all of this back-up computer Lithium Battery info.  Is to be aware if you disconnect the main power you should not trigger 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….and who knows what else?

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