To elaborate, Aristides; the solenoid has two coils, alternatively powered (lock/unlock) with a common ground. Solenoids are also very robust, so the switch could be held for some time without solenoid damage.
On later models a control unit was introduced in the driver’s door (externally identical to the solenoid) - operated by the door key. The control unit used capacitor discharge to control the relays, discharging to the appropriate relay as the door key was moved to lock/unlock. Turning the key, levers connected to the control unit, moved its ‘insides’ in the appropriate direction…
Capacitors being discharged (a second or two?), they were recharged automatically with the control unit in the new position - ready for the next sequence…
When motors were introduced (Kiekert), they require polarity reversal - which the control unit delivers, polarity as appropriate, directly to the motors. However, motors have no end-stop power cut-out, so to avoid motor burnout, the control unit delivers a 2 second burst of power. Enough for motor full travel, to lock and unlock. A failed control unit may deliver longer pulses, which in principle should blow the fuse as the motors bottom and current increases…
Again, rods operate the control unit as the door key is turned. But when remote ‘lock/unlock’ was introduced (option with the xj40), the control unit were combined, internally, with a motor. The control unit in either case is externally identical to the plain motors - except for more wires. Also, the mounting of both solenoids and motors (Kiekert) are directly compatible. With remote; the driver’s door motor is activated by the signal - and move the control unit internals to operate the door locks…
All aftermarket systems operate the same way (more or less…), but the mounting requirements may differ - and may or may not include the boot locking motor. And they usually have the option of remote or ‘local’, the latter somewhat cheaper - but the ‘remote’ set-up may be used for ‘local’ operation, leaving the control unit motor unconnected…
In short; the original set-up had no control unit (or solenoid) in the driver’s door - but the mounting and wiring were likely present and correct. So to go key operated central locking; a control unit, and the relevant rods, must be installed, or verified present. I reserve my opinion on the use of motor ‘control unit’ for solenoid relay operation - though your suggestion of using diodes seems feasible…
However, for remote operation both a ‘control unit’ and a motor is required for the driver’s door.
As a couple of asides; swapping the solenoids for motors will be eased by using the (very expensive) Kiekert set-up, including the xj40 control units as direct swaps. I swapped to aftermarket motors - and as Jochen aptly says; both ways is an awful lot of work. Particularly since the the aftermarket motors had different mounting holes…
So Jochens proposal of restoring the original is good advice - unless time and inclination strongly leans another way
Frank
xj6 85 Soc Europe (UK/NZ)
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