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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53901
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Trying to find a short in my s500 i cant get to the fuses in

Customer Question

trying to find a short in my s500 i cant get to the fuses in the back
Submitted: 1 year ago.
Category: Mercedes
Expert:  Don 'Mo Lurch' replied 1 year ago.

Not enough info submitted by customer:

please supply more info about your S500??
Why can you not access the Rear Fuses?


Customer: replied 1 year ago.
2000 s500 w220
Customer: replied 1 year ago.
I am trying the disconntct the alarm fuse in the back and I can't get to the fuses. I have opened the light underneath the back seat
Customer: replied 1 year ago.
There is a short somewhere whenever I lock all the doors the battery drains
Customer: replied 1 year ago.
Why did you refer me instead of answering my question
Expert:  Don 'Mo Lurch' replied 1 year ago.

Do you have the Lower seat removed in the rear?
which seats do you have?

Customer: replied 1 year ago.
I did remove the seat
Expert:  Don 'Mo Lurch' replied 1 year ago.

I am trying the disconntct the alarm fuse in the back and I can't get to the fuses.
IF you have the Right Rear Lower Seat removed, then why can you NOT access the Fuses?

Expert:  Don 'Mo Lurch' replied 1 year ago.

IF you have a sustainable Draw, then you need to Draw Test, rather than guessing:

Turn Ignition off

Roll driver window down
Close all doors

Using a "Multi Meter (VOM)

Remove the negative side battery cable from the negative battery terminal.
The meter needs to be able to read at least a 2 -5 amps for this test to work.

Attach a multimeter(set the dial on the multimeter to measure Amps as per multimeters instructions) between the negative cable and the negative battery post.

Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".
If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
Go to the fuse panel(s) and remove fuses, one at a time.

Pull the main fuses (higher amp ratings)last.

Perform the same steps for relays found in the fuse panel.

Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.
Watch for the ammeter to drop to acceptable drain.

The fuse that reduces the drain is the draw.

Consult the owners' manual or service manual to find what circuits are on that fuse.
Check each device (circuit) on that fuse.

Stop lamp, heater, etc. to find the drain.
Repeat steps to test your repair.

You can also try unhooking the big wire from your alternator.

The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator's power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal.

Make sure to read the ammeter before and after unplugging your Alternator

Customer: replied 1 year ago.
It only drains when I central lock the car so there's no need for me to go through the entire electrical system. I only need to test those fuses that are related to the central locking like the alarm- how can I disconnect the alarm? And how can I pull the fuses related to the alarm- I can't seem to reach the fuses in the back
Customer: replied 1 year ago.
I'm back to my original question how I can get to the back fuses. I have already take out the back seat and the light cover under passeneger rear
Expert:  Marty replied 1 year ago.

Hi, perhaps I can help. The fuses are accessed through the opening for the footwell light. Move the passenger front seat all the way forward and use needle nose pliers to reach in the opening to remove each of the fuses. This is the way we always access the fuses. If you cannot reach the fuses for some reason you will need to remove the rear SAM in order to access the fuses. I've attached the instructions below.

Customer: replied 1 year ago.
I don't see any fuses through the light hole- I just disconnected the 4 wire adapters that I could reach but not I can't. Lock my doors electronically
Expert:  Marty replied 1 year ago.

The fuses are in there. Perhaps someone has not mounted the SAM properly and you cannot see them. Can you send me a picture of what you are seeing? I'm assuming that you are in the US and have a left hand drive car. If you have a right hand drive car they will be on the opposite side.

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