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The pre fuse box by the battery has a few fuses on the outside, however INSIDE it has a relay. Does anyone know what that relay controls?
Mercedes do NOT sell this relay separately however i managed to get one from a breakers as mine had gone.
Now the car is doing some strange things. Its been sat for a week.
I started it fine. Turned it off then it was comeatly dead. Even the hazards wouldnt work. Battery had voltage but it showed a big voltage drop at the pre fuse box.
Its now sat on trickle charge and its dead then its fine then its dead then its fine. When its running its fine. Its also sporadically just lighting up the dash even though the key isnt in it or near it!
Im confused as to what that relay actually does as this may shead some light on the situation
also when the car is "dead" puting the key in the ignition wakes it up
The pre fuse box by the battery has a few fuses on the outside, however INSIDE it has a relay. Does anyone know what that relay controls?
Mercedes do NOT sell this relay separately however i managed to get one from a breakers as mine had gone.
Now the car is doing some strange things. Its been sat for a week.
I started it fine. Turned it off then it was comeatly dead. Even the hazards wouldnt work. Battery had voltage but it showed a big voltage drop at the pre fuse box.
Its now sat on trickle charge and its dead then its fine then its dead then its fine. When its running its fine. Its also sporadically just lighting up the dash even though the key isnt in it or near it!
Im confused as to what that relay actually does as this may shead some light on the situation
also when the car is "dead" puting the key in the ignition wakes it up
I don't know about the relay but if there is a big voltage drop between battery and the box you probably have bad connection somewhere in the cable feeding the box from the battery.
I have not looked at my boxes but normally there is a bigger wire that feeds the box so this wire should have the same voltage coming to the box as the battery has.
I don't know about the relay but if there is a big voltage drop between battery and the box you probably have bad connection somewhere in the cable feeding the box from the battery.
I have not looked at my boxes but normally there is a bigger wire that feeds the box so this wire should have the same voltage coming to the box as the battery has.
The voltage drop was down to the relay. Im just trying to work out what it does and why on earth mercedes dont sell it separately! Id like to work out why it went bad. Only spotted due to a heat mark on the case. We tried to saulder it but the case had melted so it couldnt make connection. The part doesn't even show on the mercades parts list (called them up) you have to buy the full pre fuse box at £695 but the only thing that had gone was a £8 relay!
Just driven 4.5 hours no issues no warning lights. Stopped twice.
The voltage drop was down to the relay. Im just trying to work out what it does and why on earth mercedes dont sell it separately! Id like to work out why it went bad. Only spotted due to a heat mark on the case. We tried to saulder it but the case had melted so it couldnt make connection. The part doesn't even show on the mercades parts list (called them up) you have to buy the full pre fuse box at £695 but the only thing that had gone was a £8 relay!
Just driven 4.5 hours no issues no warning lights. Stopped twice.
If the voltage drop was “to the relay” changing the relay does not fix anything but, if the voltage drop is “from the relay” then the relay is the problem and seeing the picture of the burnt relay points to this way.
Relay failing like this indicates that higher than rated current went thru the relay. Usually they fail with contacts going bad over time not passing full voltage thru.
If the voltage drop was “to the relay” changing the relay does not fix anything but, if the voltage drop is “from the relay” then the relay is the problem and seeing the picture of the burnt relay points to this way.
Relay failing like this indicates that higher than rated current went thru the relay. Usually they fail with contacts going bad over time not passing full voltage thru.
So could it be because the battery was low or did it get a spike in current?
Id still love to knkw what this realy is in charge of, but as its inside the fuse box it doesnt appear on any diagram!
I suspect the valtage drop was FROM the realy as the battery was at 12, at the teminals on the pre fuse box AFTER the relay it had a drop of 9v and we only had 3 at the alternator.
04-16-2021, 03:52 PM
