Installation of keyless remote control locks to SII cars

Hi all,

this is a summary of the lengthy “Generic keyless entry on SII?” thread in two parts. It intends to assist people wanting to add a modern and practical feature to SII cars:

Part I

Costs: around 25 EUR
Difficulty: 1 out of 5
Time: 3 hs
Tools: Screwdrivers, some wires, female connectors with couplings, DMM

For all SIII owners: SII cars do not operate the power locks from the doors; instead you have to open the doors with a key, enter the car and then operate the power locks from a switch that is mounted at the location of your sunroof switch at the center console. Note that the trunk lock is not powered.

As much as I like the charm of the original setup - someone said that in the 1960s no gentlemen would not have opened their passengers’ doors first anyhow -, I’d prefer the opening and closing procedure of today as a matter of practicality.

This is the flow diagram of the door lock circuit:

You notice that door lock switch (Lucas SA 178; #260 in the wiring pattern) is only supplied by one brown/blue power wire. Power is led into the switch via the post #4 and leaves the switch either not at all (center position) or to operate the opening (orange/green, post # 6) resp. closing (orange/red; post # 1) door lock solenoid relay (258). It is not a pulse switch, but lets current flow as long as it is depressed. The system relies on the spring pressure inside the switch, moving it to neutral, once the pressure is gone, and on the lack of motivation to keep depressing a switch once function has been achieved. Power on orange/green resp. orange/red in turn operates the two door lock solenoid relays situated right in front of the rear seat bench. One brown/blue wire is connecting the door lock solenoid relays leaving from post # 4.

The particular switch used in SII cars makes it very easy to install an aftermarket remote control system as it is possible to piggyback the remote signal receiver into the wires available at the door lock switch anyhow. The posts on SII switches are (different from SIII switches) simple spade connectors. In particular, there is no need to dig into any of the doors.

There are many remote control systems around, most at very reasonable prices, but also frequently adapted to much more advanced technology, mostly including the operation of a car alarm and signalling sounds/lights.

The most simple way to operate these relays seems to be a two-channel RC switch though. As I could live without any extra features I went this way.

It is necessary (a) to have two independent channels to operate both relays. (b) The RC switch needs at least to offer a possibility to choose between switched and momentary operation. (c ) the RC switch must be adapted to 12 V DC, as it is fed from the car’s power supply. The capacity of the switches should be sufficient as they only have to switch the trigger circuit of the original relays. (d) In Europe such RC units operate at 433 MHz, in the US at 315 MHz. As they are radio controlled the mounting position is immaterial.

(to be continued)


75 XJ6L 4.2 auto (UK spec.)

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Part II

I finally opted for a system (bought through ebay, but from a domestic importer at approx. 25 EUR) that is based on a KL-K201C circuit board. This is what it looks like (of course, it comes without the wires attached …)

and this is the diagram of it:

Now what does this mean: Though it is powered by 12V DC the system is able to control all kinds of electric power circuits: It can handle DC or AC, 12V or 240V, turn on or turn off. To imitate the function of the original door lock switch it has to be configured as follows:

Operation mode needs to be set on “momentary”: the respective switch is operated as long as the buttons are depressed; operation ends when the button is released. To achieve this you do not use the connecting pant that comes with the switch and is used to either connect S1 and S2 (for “toggle”) or S2 or S3 (for “latching”).

As the energy needed to power the relays can’t (yet) be transferred through the radio signals of the sender, the switch needs power supply for its own function (top two posts).

The following six posts relate to the two channels: B1, G1 and K1 for channel 1, operated by button A on the sender; B2, G2 and K2 for channel 2, operated by button B on the sender.

There are three posts for each channel because the switch can either be used to cut off a permanent flow of current or to turn on an otherwise unpowered connection. This is expressed by the descriptions “normally open” (meaning there is no continuity as a rule) for K and “normally closed” (meaning there is continuity as a rule) for B. In our case we want to operate the door lock solenoid relays and put power on wires that are normally unpowered, so we’ll use the “K” posts.

Otherwise the switch module is nothing but a switch. So there has to be a line in (these are the “G” posts) and a line out. As in our case we want to switch power on we need to feed power into the “G” posts and use the “K” posts as switched line out. Ignore the confusing drawing in the right part of the Diagram!

Starting from this the connectors have to be used as follows - starting from the top connector:
-: ground
DC12V Input +: the brown/blue wire
B2: not used
G2: the brown/blue wire
K2: the orange/red wire operating the closing door lock solenoid relay
B1: not used
G1: the brown/blue wire
K1: the orange/green wire operating the opening door lock solenoid relay.

The next step is getting appropriate automotive electric wires, ideally in different colors which I didn’t get, and making up a little wiring loom.

I used coupling connectors permitting to connect with the spade connectors on the rocker switch and connect the original wires on the male couplings. As three wires have to be supplied with power by the brown/blue wire I tapped the DC12V + wire twice to feed into G1 and G2. Finally, I protected the wires where they exit the switch module box and tagged the ends to identify after the box has been closed. This is what it looked like:


You may be a bit more generous about the length of wires than I was, as the switch is easier to connect with an extra inch or two. As there is only a thermal breaker upstream it might also make sense to put an inline fuse before the RC switch module.

The next step is the preparation of the sending operation. I used a small DC transformer from an electric model train set that I set at 12.6 V (controlled by a DMM) and supplied the circuit board with power. One of the red LEDs comes on. Now when you depress the learning button on the circuit board the other LED will start flashing and tell you to operate one of the buttons on the sender. Then the second LED will extinguish. You then can control the functioning of the switch: depressing the buttons on the sender should result in clear clicking sounds of the two relays on the circuit board. If you connect a test light to the K posts you can confirm operation under load (in my case the first attempt failed; only a second attempt helped to program the receiver). Once it all works you can close the cover of the switch module.

The last step is to install the thing in your car: First you prise off the part holding the window rocker switches. Then you undo the two screws at the front edge of the center console liner. Then you undo the bolt at the front upper trailing edge of the “ski slope”. Now you can lift out the center console liner. From the downside (!) you can access and depress the four tabs at the door lock switch body and push the switch out in upward direction. Take notes of the colors and position of wires and pull the wires.

The switch module box then goes into the “cheek” of the centre console rear of the switch. The wires must be led forward underneath the metal support.

Then get a good ground - I cut the ring connector that you see at the black wire in the picture above open to be C-shaped, loosened a screw in the floor pan next to the gear box lever unit and pushed the C-ring around the screw before tightening it again.

Now the time has come to connect your + wire with post #4 on the switch, the K1 wire to the rearward facing (# 6) and the K2 wire to the forward facing (# 1) post of the switch. Then reconnect the original wires on the male couplings of the connectors you used: orange/green on # 6, orange/red on # 1, brown/blue on # 4. Don’t forget the extra brown/blue wire supplying the door lock solenoid relays and sitting on post # 4 as well. It is going to be pretty tight on this post.

Finally, try to fix the switch module box to the cheek of the chubby box. Ideally, you have butylene rubber to stick it in place; I used duct tape which is a bit of a mess in the narrow space available.

Test operation. Now the door locks should be operated both by the original rocker switch just as before and upon depressing the buttons on the sender unit.

If the system functions as supposed, the liner goes back in place; the front two screws are fixed; the upper bolt goes back and the window rocker switch plate is put back in place.

Enjoy your remote control.


75 XJ6L 4.2 auto (UK spec.)


Mr Jochen,
Thank you! Your post will go into my library for future implementation. You have made this job much easier and it would be handy upgrade.