1984 300DT: where is the anti-theft master control unit located?

[merc lover]

Trunk lock will not unlock allowing me to open the trunk. Per other forum members advice on another thread, I am trying to locate the anti-theft master control unit. I've attached two photos, first photo is of two silver boxes under the instrument panel on the left panel on the driver's side. The second photo is of a silver box just above and to the left of the brake pedal.

I need to bridge pin 8 and pin 5 (brown and green wires) to see if this will disarm the alarm and open the trunk lock.

Any ideas which of these silver boxes is the anti-theft master control unit?

[Hogweed]

i might be mistaken but the trunk lock is mechanical on that car and turning the key in the correct direction and pushing the button in, it will open. i don't know how antitheft (esp 1984 trim) would stop the lever from going where it's supposed to go. the valet key won't open the trunk, which you probably know

Originally Posted by merc lover

Trunk lock will not unlock allowing me to open the trunk. Per other forum members advice on another thread, I am trying to locate the anti-theft master control unit. I've attached two photos, first photo is of two silver boxes under the instrument panel on the left panel on the driver's side. The second photo is of a silver box just above and to the left of the brake pedal.

I need to bridge pin 8 and pin 5 (brown and green wires) to see if this will disarm the alarm and open the trunk lock.

Any ideas which of these silver boxes is the anti-theft master control unit?

[dude99]

anti-theft master control unit.

No such part exists on your car. The locks are vacuum operated. I believe the w124 was the first to offer a factory alarm, however it too used vacuum for locks. There is no electronic component that should stop you from opening any door\hatch\trunk on a w123.

[merc lover]

OK, the other option is to hook up either a mity-vac or a vacuum pump to a vacuum line connection on the passenger's floorboard to see if that will open the trunk. When I turn off the engine, I then lock the car doors using the key in the driver's side key slot. When I unlock the car doors by using the key in the driver's side key slot, I normally HEAR the trunk also unlock. That is not happening now which makes me think the problem is:

A. Bad trunk vacuum actuator.

B. Bad fuel door vacuum actuator.

C. Failing vacuum connector somewhere in the system.

D. Leaky vacuum reservoir.

So I thought I would start by hooking up a mity-vac to the vacuum line connection on the passenger's floorboard to see if that will open the trunk. I'll keep everyone posted.

[merc lover]

Strangest thing; I just went out to try it one more time. The car has been sitting at least six hours since I ran the engine. I placed the key into the driver's side door key slot and unlocked the doors. All four doors immediately unlocked.

After a few seconds I then heard both the fuel door actuator and the trunk lock actuator unlock. I then unlocked the truck as normal However, it was a much longer amount of time to hear both the fuel door and the trunk to unlock which makes me believe I have a leak SOMEWHERE.

[tyl604]

Leaks are pretty easy to find though. If yours is like my SD, all you need to do is pull up the carpet on the passenger front floor and find the channel with all the vac lines. Start blocking them off and introducing the mityvac on one line at a time and you should be able to find the leak.

I traced a leak in mine to the rear driver's side door actuator in a flash.

[Diesel911]

There are W123's that have an anti-theft system. Assuming they were Mercedes ones there is supposed to be a pull cable to open the trunk on under the bottom drivers side back seat.

The red arrow in the diagram points at the pull cable.

[merc lover]

I forgot to share that this afternoon I tried the emergency cable pull located under the rear seat. I had a helper try and open the trunk at the same time I pulled hard on the emergency cable pull. The trunk would not open.

So, weirdly enough, after sitting six hours the trunk opened! I am going to follow tyl604;s advice to track down what appears to be a vacuum leak. Seems to happen on these cars from time to time.

[Hogweed]

a non-valet key should still operate the lock mechanically regardless of a vacuum leak

[tyl604]

Agree with Hogweed. That key has a round plastic grip instead of a square grip.