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From digest.v7.n244 Tue Sep 23 12:37:17 1997
From: Jim Cash <>
Date: Tue, 09 Sep 1997 08:00:37 -0400
Subject: Re: Re Central; Locking - E28


Just some additional information - so as not to mislead you.

I can't remember which year you had, but I know it was not an 82. My drawings are for 82, and while I think they will be the same, they might not.

I saw a note from another person to you mentioning the key lock unit itself.

I do not think it has electrical connections, but then I am working from knowledge about an 82. I also gave you some contact information about the actuators - I kept this simple but the following is more precise.

Here is how the 82, and I assume your, system functions.

The key locks are mechanical and are independent of the electric locks. But they are physically linked at each door and the trunk so that the actual lock mechanism is controlled by the combination of the key & electrical actuator linked together. When you turn a key you are not only locking/unlocking that door physically, but also moving the actuator for that door - which then sends a lock/unlock "request" to the control unit. The control unit then sends the appropriate lock/unlock "signal" to all the actuators (in parallel), which use a solenoid to produce the same movement in the locking mechanism as does the physical key lock.

Each actuator is actually a double unit.

  • - the internal "request" contacts that send ground to the control

    unit on the "lock request" and "unlock request" leads.

  • - the solenoid (motor) which actually moves the locks electrically.

When all actuators are in the same position (locked or unlocked) the system is at rest. As soon as one actuator is moved (i.e. moving the solenoid from unlocked to locked position) now a ground appears on the lock request lead to the control unit - which reacts and sends a "lock signal" to all actuators. If they all respond and go to their locked position, then their associated request switches are now grounding their "lock request" leads. Since the system is already locked, and since there are no grounds on the unlock leads - all's well.

But if one of the actuators fails to operate, or if one of the internal switches has failed then you immediately get a ground on the opposite lead. Depending on the nature of the fault it might affect only the locking, or the unlocking operation.(i.e. a switch shorted in the unlock position will allow all the locks to unlock, but will not allow them to lock.) If this is intermittent due to a slow acting actuator, or corrosion in the switch, then you will get both situations, at times.

The contacts on each door actuator are as follows:

  1. - solenoid motor - lock signal from control unit - contact #1 - blue wire.
  2. - solenoid motor - unlock " " " " - " #2 - white wire.
  3. - request switch - lock request - sends ground to control contact #7
    • - yl/blue.
  4. - request switch - unlock " " " " " " " #6
    • - gn/blue.
  5. - shown "unused" on mine but I think it goes to alarm circuit.
  6. - request switch - ground connection.

The trunk is the same except that the function of contacts 3 & 4 are reversed (this might be a typo).
Also the wires and connections at the control unit are different as follows.
3. - request switch - unlock request - ground to control contact #9 - yl/black.
4. - request switch - lock " " " " " " #8 - gn/black.

The drawing shows the lock request leads from the doors, and the trunk then connecting together in the control unit. While this makes sense functionally it does not account for why you can sometimes use the trunk unit when the doors will not work. I suspect that the drawings not completely accurate inside the control unit.

The control unit also has and internal "automatic unlock" switch that initiates an unlock request should it sense an "impact" greater than 5 g. This is what unlock your doors in an accident. I remember hearing that it also reacts to a roll over - never tried it. That switch is powered in "Run" and "Start" positions on contact #5. It is not powered when car is off so that you can not unlock a car by running into its bumper (impact) - yes some of the older ones work this way.

In case you are interested, I found it very useful to have a toggle switch on the console (just below and to the right of the shifter) to operate the locks. I just drilled through the little plate to the right of the automatic shift - it pops out) and mounted a double throw toggle switch. I connected the centre pole to ground and the other 2 leads were connected to the lock & unlock request leads that go to the control unit. You can splice into them up under the dash a various places - or you can go right to the control unit.
Suggest you mount the switch so that pulling it back causes a lock request. That way you can get in the habit of locking the car as you shift into gear, and unlocking as you shift to Park.

Hope this, and previous info helps you find your problem.


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