MB Cruiser Battery Connections


Hello All;
My Sprinter has been sitting for a while and the "engine" battery has died. After 24 hr on a charger, it only reads about 3V. Ive ordered a new Deka AGM battery due to arrive later this week, but I want to tap the accumulated wisdom of this site to help me understand the various connections and devices associated with this battery before I disconnect it. Any help is appreciated. While Im mostly familiar with the !2V system in the camper, Ive never touched anything electrical in the engine compartment.
This is the engine battery:
Is the item at (1) some sort of protectivie fuse link in the 12V+ wire?
The item at (2) appears to be some sort of combiner. The lowest cable (3) must go to the house bank, its at 13.4V.
One of the cables above that comes from (1), the other (4) might go where?
The red wire with the yellow crimp has continuity with ground as does the adjacent blue taped lead.
Im guessing that (1) and (2) were installed as part of the camper package by Forest River?

This next picture is a detail of the positive battery terminal:

Is the red-taped cable to the left the main engine/starter lead?
The top unmarked cable to the right goes to (1) in the other photo.
What might those lower four red leads go to? Are they part of the camper fit out?

Thanks for looking. If anyone can offer suggestions, Id appreciate it. Is there a base T1N 2500 wiring diagram available anywhere that might help me understand what Im looking at?

Apologies in advance if Ive screwed up the post or the photos. This is my first post in a long time and my first experience with this newer forum software.


Erratic Member
Your numbers didn't appear on your photos. Whoops ... i didn't look far enough away from the battery...
Those numbered items are all NON-original (i.e. not MB/Dodge/Freightliner) wiring ... they're RV-related.
The black wrapped wire at the battery's positive post (not shown in figure below) could be the feed to the isolation relay to allow the Sprinter to charge your house bank. Your item (2) may be that relay.

The black box on the battery positive post is the "power distribution center" (PDC), or "pre-fuse block".
Here's what it feeds: The four red wires are all MB originals ... not RV related.

Yes, the big cable with the red wrap is the starter cable.

Here's a 2006 service manual: http://diysprinter.co.uk/reference/2006-VA-SM.pdf
Much documentation is here: http://diysprinter.co.uk/reference/
And that PDC diagram came from here: http://diysprinter.co.uk/reference/T1N_service_scans/

It ALWAYS helps if you tell us your model year....

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Active member
Item 2 looks like a battery isolator. When the isolator receives power signal that the engine is running it combines both the starter battery and coach battery so you alternator charges both while underway. When engine is off, it isolates the two batteries so that as you draw down your coach battery running 12v appliances and such it does not also drain your starter battery so you can still start the van.


Thank you both for your responses. Yes, I should have mentioned that its a 2004 Dodge/Freightliner Sprinter with a 2005 Forest River MB Cruiser camper build. Ive changed a lot of the camper build electrical, replaced the converter/charger, but done nothing upstream of the converter/charger.

I plan to disconnect the house battery and shut off the solar charge controller before doing anything. Anything else I should do before removing the dead battery? Or is the damage (if any) already done?


Also, there is a similar item to (1) between the converter/charger and the house bank inline on the pos cable. Its got a tiny reset button on its side, so Ive assumed its some sort of circuit breaker or surge protector.


UK 2004 T1N 313CDi
Does item (1) have two small wires coming from it? It looks like it has from your photo. If Yes then it is a current shunt, or measuring device, for some control panel function.



You need to find out which cable does what.

I need to know where wire #3 and #4 go to. One is the house battery. The other is 12 volt feed to control panel. Currently. I think your wiring is done wrong.

Unhook wire number three. See if you have power to your control panel.

Unhook wire #4 and see if it has power from your house battery.

Item #1 looks like a auto reset circuit breaker.
Relay #2 is used to charge house battery while engine is running. The brand is white rogers. It is a 100% duty cycle. 100 amp rating.

Does your house battery have one positive wire coming off it or two positive wires?

Does it have a battery to battery charger in the system. By the way it wired I bet it doesn't.

I just went threw this a couple of weeks ago on my van. It was not built as a camper. It was outfitted with 12 volt / 110 volt panel as a work van. My wiring is almost the same. It was wired wrong.


Erratic Member
I plan to disconnect the house battery and shut off the solar charge controller before doing anything. Anything else I should do before removing the dead battery? Or is the damage (if any) already done?
When removing the starter battery, disconnect the negative post *first*.
That makes the positive post "safe", in terms of it won't try to weld your wrench to the frame (or any other piece of metal) if you slip a bit and make such contact.

2nd safety hint: wear gloves, wrap with tape or remove all rings (etc) so that they won't make such contact.



Thanks again for looking. Good info.
This engine DieHard battery is dead (3V) Cable(3) is at 13.4V with the house bank floating on shore power charger, so (3) must charge house bank when charging voltage exists at (2). PhillipE, I too would like to know where (4) goes. When you say control panel, are you referring to Sprinter panel or RV panel? There really is no RV panel, per se, but a fuse panel associated with the charger/converter, and fed by the house bank. There used to be a Onan generator, but I removed it several years ago. Maybe (4) was the power for the generator starter? Could you be a little more specific about what was/is wrong with your/my wiring? You are right, no B to B charger that I am aware of. You must be correct about (1), it looks exactly like several CB's that come up on a web search. There is no reset button on this one, but there is a reset button on the one on the house bank pos lead.

Autostaretex, yes, great reminders. I knew to disconnect neg first, but could easily forget in haste. Thanks for the reminder.

I seem to recall reading on here that the Sprinter "computer" can be damaged by letting the battery go to zero. Hope Im making that up, because this has been sitting for several months in this state. I do recall that when the DieHard was installed at Sears while we were on the road some years ago, that the dash lights and functions were absent upon startup. The mechanic said there was some fault of the vehicle and he couldnt fix it. My wife said "maybe its a fuse?". After huffing and puffing, the mechanic checked the fuse block under the driver seat and guess what? It was a fuse. She never lets me forget it! (Nor should she)


Erratic Member
The T1N Sprinter can get mightly confused as the battery voltage disappears into the mud.
But once the new battery is in place, by the 2nd start all confusing *active* faults will have been cleared.
The Check Engine (MIL) light should self-extinguish.
It may *remember* (i.e. stored faults) its previous confusion, but (after verifying that none are really active), any scanner should be able to clear them.



Have shore power disconnected. Unhook cable #4. If you loose 12 volt power to the RV distribution panel. Then that tells you where #4 cable goes.
You can do the same thing with a volt meter and a long wire with gator clips and OHM test #4.

The same way with cable #3, I bet it goes to the house battery bank.

If those cables go to the places I think they are going. Then your house bank is not doing anything. All the RV 12 volt is coming off the starting battery when the engine is not running. That relay is isolating the house battery from the RV when the engine is off.

When you find the location of #3 and #4 post back.

If those cable go where I think they do. Remove cable #4. move it down and attach it where cable #3 is located. Leave cable #3 at the same terminal. That will tie the house battery into the RV and isolate the start battery to the vehicle only.

I bet the generator used the house battery for starting. RV/ body building companies tried to stay way from the vehicle side of wiring as much as they could.


New battery is installed and all functionality restored. No problems at all with Sprinter instrumentation. Had to reset the stereo display, its powered from the house bank.
#3 cable confirmed to the positive buss at the house bank. #4 is still a mystery. With the house battery disconnect off, charge controller off, engine off, there was no power to the house12V fuse panel. Fuse panel is fed from the house bank pos buss.
Old DieHard battery was two weeks short of seven years old, the last of which it sat unused.
Thanks again for all of the comments above.

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