W211 E270Cdi, 2004. Battery disconnected and boot locked. Help!!

[james2747]

Had a number of jobs to do on the car.
Replacing the front flexi brake hose .... and bleeding brakes all round plus removing headlight to fix adjuster screws, so thought it wise to disconnect both the main battery and SBC battery before I started. Have disconnected both batteries in the past to recon them using a smart charger and had no problems.
I made sure car was unlocked before disconnecting battery.
All went well till a few hours later, I wanted to get in the boot to re-connect the main battery.
I was expecting just to use the standard metal key in the boot lock ... as I'm sure I've opened it that way in the past.
NOT THIS TIME. Nomatter what I tried the boot lock just wouldn't open .... key turns 90 degrees but seems if that is dead locking it rather than trying to unlock it. The lock is in good condition, gets a squirt of WD40 a few times a year so its deffo not seized.
Is there any way I can get power back to the car without opening the boot .... I'm sure some cars have a +'ve and earth connection under the bonnet where you would connect up a charger. so I could then try to get it to unlock by pressing 'unlock' on key fob
Failing that, is there any other way I can get the boot open?

 

[grahamcol]

Well all of my various Mercs have had a little black box under the bonnet on the nearside approx 1/3 of the way from the windscreen to the radiator. The box has a lift up lid and underneath is the positive terminal. Use that and any body point for the negative. Good luck.

 

[onefortheroad]

Had a number of jobs to do on the car.
Replacing the front flexi brake hose .... and bleeding brakes all round plus removing headlight to fix adjuster screws, so thought it wise to disconnect both the main battery and SBC battery before I started. Have disconnected both batteries in the past to recon them using a smart charger and had no problems.
I made sure car was unlocked before disconnecting battery.
All went well till a few hours later, I wanted to get in the boot to re-connect the main battery.
I was expecting just to use the standard metal key in the boot lock ... as I'm sure I've opened it that way in the past.
NOT THIS TIME. Nomatter what I tried the boot lock just wouldn't open .... key turns 90 degrees but seems if that is dead locking it rather than trying to unlock it. The lock is in good condition, gets a squirt of WD40 a few times a year so its deffo not seized.
Is there any way I can get power back to the car without opening the boot .... I'm sure some cars have a +'ve and earth connection under the bonnet where you would connect up a charger. so I could then try to get it to unlock by pressing 'unlock' on key fob
Failing that, is there any other way I can get the boot open?

Use the fag lighter and feed 12v into it. You just need a plug with the 2 wires and a spare battery.

 

[Blobcat]

Use the fag lighter and feed 12v into it. You just need a plug with the 2 wires and a spare battery.

The 12v socket is normally ignition switched

 

[Chrishazle]

On my S204 the only ignition off live socket is the one in the armrest for the telephone pre-wiring, all the others are ignition on only - annoying and stupid! However, if you can open the bonnet there will be an emergency +ve terminal lurking under a red plastic cover and you can use something suitable (top of the suspension, side of the engine etc) for the -ve, connect a battery or charger to these.

 

[james2747]

Use the fag lighter and feed 12v into it. You just need a plug with the 2 wires and a spare battery.

Thanks for your reply.
Unfortunately it didn't work.
On my vehicle the ignition has to be on before cig lighter is live.
Now if I could only find the +'ve terminal that is supposed to be under the bonnet somewhere, then all would be well.
I'm pretty sure there isn't one on my car but if someone knows differently .... please shout quickly.

 

[james2747]

On my S204 the only ignition off live socket is the one in the armrest for the telephone pre-wiring, all the others are ignition on only - annoying and stupid! However, if you can open the bonnet there will be an emergency +ve terminal lurking under a red plastic cover and you can use something suitable (top of the suspension, side of the engine etc) for the -ve, connect a battery or charger to these.

Thanks for your reply.
There isn't an emergency +'ve terminal that I can see ... no metion of one in handbook or in workshop manual either.
Have seen them on lots of other cars and wifes car (Merc SLK) has one you can't miss.
I'm still locked out and I've been at it all day!!!

 

[james2747]

On my S204 the only ignition off live socket is the one in the armrest for the telephone pre-wiring, all the others are ignition on only - annoying and stupid! However, if you can open the bonnet there will be an emergency +ve terminal lurking under a red plastic cover and you can use something suitable (top of the suspension, side of the engine etc) for the -ve, connect a battery or charger to these.

Thank you for your reply.
I'll certainly have a look if there is a similar socket on the W211 as you are correct in saying that all the other sources (like ciggy lighter) are not live unless ignition is on.

 

[mersum1es]

This is covered many times... W211 sedan has NO jump start point in engine bay. Wagon model has.

But if doors are open, W211 has handy pre fuse box in passenger footwell where big live lead is coming straight from battery. There even bigger current can be feed, unlike cigarette lighter socket. BTW W211 cigarette lihgter has two fuse options; by setting fuse in another slot, lighter is feeded always, not via ignition switch.

 

[Craiglxviii]

This is covered many times... W211 sedan has NO jump start point in engine bay. Wagon model has.

But if doors are open, W211 has handy pre fuse box in passenger footwell where big live lead is coming straight from battery. There even bigger current can be feed, unlike cigarette lighter socket. BTW W211 cigarette lihgter has two fuse options; by setting fuse in another slot, lighter is feeded always, not via ignition switch.

That is a really handy thing to know!

 

[Botus]

putting the key in the boot to unlock just like one did on an old fashioned car, didn't work on my fathers nothing happened, lubed, kicked, prodded nothing....

I don't like the idea of connecting power to the car.... "Who knows if the battery positive terminal is touching earth..." you could blow up all the electrics ????