Opening trunk
 

I put my 2000 sl500 away and took out the battery to keep in the house. I went out today to get something out but the key won't open the trunk. What do I do now?

I had a similar experience with my '98 E300 diesel. I bought a new battery and put it in my trunk. I went home and took the old one out and tried to get access to the new one. The trunk would not open until I reinstalled the old one. There is something electrical; I don't know what it is.

There may be an alternative I didn't try. My key has a small metal key that is inserted into it for storage. I have been told that had I had the sense to use that metal key, I could have opened the trunk without reinstalling the battery. Try that first if you have one.

The battery for a sl500 is in the trunk and I don't know what you mean by a small metal key.

I have a fairly large plastic key that I insert into my ignition. The key also has buttons that locks and unlocks the door and raises and lowers the windows. There is also a slender metal key that is inserted into the larger plastic key. The only part of the key on can see when the key is inserted is a metal eye on the side of the larger key. The smaller key slides out when I pull on the eye.

continued:

I don't know whether your key is the same as mine.

I also have a connection under the hood of my car that allows the use of a booster battery. It is a post to which one attaches the lead from the positive post of a booster battery. The ground lead or cable from the booster battery can be attached to the manifold or any other appropriate ground under the hood. Maybe your car has the same feature.

I don't know much about SLs. I just thought your car might have these features, because they are two model years apart.

This video might help:

https://www.youtube.com/watch?v=VIe7HUL5S9I

Are you inserting a metal bladed key in the trunk button, turning then pressing the button? ( There are 3 positions so try all 3 )

That's an interesting point as to whether the under hood connection can be used to "backfeed" a car's electrical system in the absence of the car's battery. I would try it, but being aware of the possibility that the loose end of the "positive" wire which is no longer attached to the car's battery may be touching part of the car's body and would create a dead short when power is applied. Give it a go and report results.

Given the battery was disconnected, the remote won't work until it is resynced. With a single button flip blade key , press the button 2X while pointing at the receiver ( it is IR like a TV remote ) then insert the key into ignition and turn to the on position.

Regardless, you should be able to unlock the trunk with the metal key using the trunk button.

I thank everyone for the help but I felt MB with all the weird engineering wouldn't make it that difficult so here is how I got the trunk open. Put key in lock turn all the way to the left and push key forward. Done.