I think that the vac pump for the trunk lock is under the rear seat. I would try that first. Get a mityvac and find the line for the trunk. Give it a few pumps and it should pop open.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

Thanks for the suggestion. Bought a hand held vac and tried every line connected to the pump but none would unlock the truck. Then I noticed the gas cap door was latched after doing that. Now I couldn't refuel the car. (yikes)

So I took my air compressor and set the regulator down to about 30 psi and gently pressurized the line to the gas cap door. It opened! Then I pressurized the other lines until the truck push button was engaging and I could open the trunk. Turns out the vac pump for the central lock system is blowing its fuse, and of course that fuse is located in the trunk! Now trying to find out how to repair the vac pump or find a replacement.

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1999 S320
2001 E320 wagon