So I know there have been countless posts on the ML320 trunk actuator, and I've read most of them, but I have still been unable to fix my problem. I replaced the actuator AND the hatch latch (which turned out not to be necessary I guess), and still the key fob and the electronic locking mechanism doesn't lock the trunk. The trunk locks manually, but that's about it. Does anyone have any advice? I was thinking I could replace a relay, but since it is only the trunk and all other doors work fine, I wasn't sure.

Is it that you cannot lock it but you can unlock it?

It's that the only way the lock functions if it is manually locked and unlocked. When I press all doors lock on the key fob, all doors lock, but the hatch.

Had the same issue with mine. lock would twitch when I hit the button but would not lock or unlock the tailgate. Saw something posted somewhere about a weak plunger in the mechanism. I got lucky. Pulled rear panel with a fork tool. Found that the linkage had jumped out of place. Sprayed it all down with brake clean and put a few drops of gun oil on joints. Working good now.

The first thing you should do is remove relay K15 and swap it with K17 and see if things work.

Post back with results and if negative, you will have to remove the panel again to access the wiring to the actuator.

Swapped relays, no change. Cover is off; what wiring should I look into? Know a good mechanic in Brooklyn)!?!

Leave the cover off until this problem is resolved.

Fashion a 6" jumper wire (18 gauge) with spade terminals attached (trim to fit). Must use spade terminals to make contact inside fuse box.

1. With key out of the ignition, remove K15 relay. Using the illustration of the fuse box, insert one end of the jumper wire into slot #30 and test the other end for 12v.

If so, partially insert the other end of the wire into slot #87 and see if the locking motor actuates. If so remove the jumper wire. Note you are only testing this to check this circuit.

2. With the key out of the ignition (using one end of the jumper wire inserted) using a DVOM, test slot 87b for Ground, test slot 85 & 86 and tell me which one has 12v.

Post back with results to go onto the next and final test.

maj dundee

maj. dundee i got same problem here replace new actuator and still same. after i dit the test that you post here actuator works and slot 86 has 12v any ideas

cax, telling me that you have the same problem does not help. Tell me exactly what your problem is. Then tell me what you have done to try and getting it working.

Also tell me the results of the test I posted. What did you get at 30, what did you get at 87 and so on.

An old thread but I seem to have a similar issue with the rear hatch lock on a 1999 ML430. I do not have 12VDC at 30, a jumper between 30 and 87 does not actuate the lock, 87B does go to ground and I have 12 VDC at 86 but not at 85. Can you help?

sounds like rear wiring bad