Help me understand these relay diagrams, please!

ronde.van

New member
2015 Sprinter 2500, 4 Cylinder, Cargo Van

Hi all, I'm new and I've really learned a lot from all the great content on here, but I'm having trouble sorting out this MB diagram on fuses/relays

There are two things that I would like to do, ultimately:

1.) I'd like to locate my fuel pump relay so that I can build in a custom security switch to disable the fuel pump

2.) I'd like to locate my (?) starter relay (?) or other appropriate relay so that I can link my Blue Sea ACR 7622 to the ignition wire so that my auxillary battery and starter battery are isolated during cranking/starting.

Using the MB diagrams/maps I can locate all the relays, but it seems that there are multiple relays sometimes of the same function. For example, there appears to be a fuel pump relay under the drivers seat at R5, but there is also a fuel pump relay listed in the main panel to the left/under the steering wheel at R3. I've run into the same issue with trying to locate my starter relay.

Also, another source of cofusion is that sometimes it will list the relay's function, and then say that it is a terminal of some sort (e.g. R5 ; K40/9 ; Starter Relay, Terminal 50). What does terminal 50 refer to??? sometimes it will say terminal 15 or 87 or 30 and I have no clue what to make of this.

Any help will be sooooo appreciated!

Thanks in advance.
 

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autostaretx

Erratic Member
I'll start with the easy one: terminal numbers.

The terminal numbers are derived from a German industry standard that's been around for more than 50 years.
(DIN= Deutsch Industry Norm, in fractured german. One US rough equivalent is "ASA", American Standards Association)

Here's the list of what-numbers-pertain-to-what: https://en.wikipedia.org/wiki/DIN_72552

"Terminal 50" is starter-related.
"Terminal 15" is "+12 turned on by ignition switch"
"Terminal 30" is "+12v direct from battery: always hot"
(the "direct" may pass through a fuse, but it won't be switched by anybody)

Regarding isolating the two batteries during starting: under your driver's seat, you'll find a terminal strip with 3 wires feeding it and studs provided for stacking on wires for nefarious purposes.
One of those studs is "Terminal 61 (D+)" ... that becomes hot when the alternator starts charging.
During the time the engine is off or cranking, that post will not be powered.
Battery isolation is its primary use.



--dick
p.s. additional DIN number lists, some fully sequential:
http://www.bosch-classic.com/media/...switches/downloads_3/klemmenbezeichnungen.pdf
http://www.vintagebus.com/wiring/defs.html

p.p.s. regarding the fuel pump relays... what is "footnote 5" on the first list?
 
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Munmile

Member
from my experience with DIN relays:

terminal 85: ground side of relay control coil.
terminal 86: positive side of relay control coil.
terminal 87: relay contact connected to terminal 30 when control coil energized (normally open).
terminal 87A: relay contact connected to terminal 30 when control coil is not energized (normally closed)
terminal 30: relay contact to battery positive (should be fused)
terminal 31: chassis ground
terminal 50: signal from the starter solenoid when engaged.

cheers
Munmile
 

ronde.van

New member
Thank you for those replies. Very enlightening to realize that all those terminal numbers are part of a standardized code!

Footnote (5) states: "Not on vehicles with code MI6/MH3/XM0"

Those codes are defined earlier in the document as:

Code MI6 - Proconve L6 low-emission vehicle
Code MH3 - EPA 13/CARB low-emission engine
Code XM0 - Model facelift (2013)

I'm not sure if they apply to my sprinter or not...


I like your idea about using the Alternator circuit to isolate the batteries during starting. As I understand, those three posts are the "alternator running", "key in position 2 (ON)" and "always hot" circuits. Do you think that these other two circuits ARE hot while cranking, or do they temporarily cut power also while cranking?

https://www.mercedes-benz-vans.ca/f..._Benz_Sprinter_Fuse_Allocation_Supplement.pdf

There is a link to the manual I'be been referencing. I'm wondering if a Load Relief relay might be able to meet my needs? I've read that the load relief relay turns off all non-essential loads while cranking so that the starter can get its necessary amps from the battery. Do you have any experience with this?

Thanks again both of you for the help. Very educating!
 

autostaretx

Erratic Member
The other two terminals on the strip do NOT power-down during cranking.

(a weak battery may cause their voltages to drop (to perhaps 10v), but they don't go Off)

--dick
p.s. i think you're a likely candidate for both:
Code MH3 - EPA 13/CARB low-emission engine
Code XM0 - Model facelift (2013)

Enter your VIN at http://carinfo.kiev.ua/cars/vin/mercedes/vin_check
and you'll see your "datacard" ... what MB built into *your* Sprinter.

I don't have a 2015's datacard to look at (hint, hint) to cross-check (a 2011 had MH1, and pre-dates XM0)
CARB is California Air Resource Board, i.e. the emission standards required for a 50-state engine.
 
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