First things first, get yourself down to a scrapyard and source the actuator, pedal, ECU etc. Should be relatively easy to find if you browse EYP for car breakers. The actuator mounts on the RH inner wing just behind the headlight. (Photo). There should be a 4-pin connector on the loom behind the headlight which fits into the actuator connector, check the wiring colors on the circuit diagram. Also the actuator has a vacuum pipe which feeds from the Y-piece just above the throttle body. This is quite simple to connect, and is shown here. That's it for the actuator itself, the cable comes later.
Next you need to consider the wiring.
If your car does not have electric seats then you will have a spare
switch on your RH facia panel, which has wiring behind it for the
electric seat switch (circuit diagram).
These run to C85(LG/W) and
C87(W/O), both of which are under the dash near
the fusebox (photo).
C85 can be
altered to suit the cruise control setup. Firstly it is prised apart
and the LG/W wire cut and moved to where the UO wire should be which
feeds the cruise control - NOTE: the connector diagrams are pictured
looking into the connector, ie not from behind which was what I first
tried (D'oh!). This is then connected to the WO wire from C87 (make
sure you get the right end - pull the connector apart and test the
continuity to the facia switch). Next the LG/Y wire can be cut and
connected to the LG/W wire going to the facia switch. That all sounds
more complicated than it actually is, you are really just connecting
the LG/Y and UO wires from C85 to the facia switch wiring which is
present for the seat. (facia connector - LH
half shows existing seat wiring, RH half is for cruise when fitted
to Sterling from new. Connector wiring for
fastback models, although seat wiring is usually present in LH
part of connector. These both live here.)
That should then take care of the switched supply of power to the cruise ECU on the UO wire. If you have no spare switches you should be able to just wire this up permanently as the cruise control always switches off when you touch the brakes (or clutch) anyway. The next step is the ECU itself, its connector (C312) is buried right under the dash next to the relay tower here and is quite difficult to get at. I moved the connector for mine and repositioned the ECU so it is held in by the fusebox cover panel, I will probably move it once I am satisfied it works OK.
Steering wheel switches. The models equipped with cruise control had two little buttons at the bottom of the steering wheel for 'set' and 'resume'. The tracks to support these are present in all of the steering wheels, so they could be fitted to a normal steering wheel. This is what I intend to do unless I come across another good condition wheel cheaply. You will need to change the steering wheel slip-rings though, as the standard one just feeds the horn with a single connector. Remove the steering wheel and pull the old slip ring and its spring piece from the wheel and column respectively. The horn connector goes to the single connector on the new slip rings, and the cruise connector should be on top of the steering column somewhere with a 2 pin connector to connect to the other part of the rings. The rings then position carefully under the wheel with the 2 studs located and the 3 connectors protruding from the hole. Connecting up the horn and set/resume switches is then quite straightforward using the circuit as reference. Here is a real steering wheel with cruise fitted.
Now you have everything in place except the control cable. This needs a different pedal assembly, which has two cable connections and a mechanism for pushing the pedal down from the cruise actuator. This is a simple replacement for your existing one, and the cruise cable goes through a hole in the bulkhead about an inch above the throttle cable and connects to the top of the curved part of the pedal assembly. The other end then attaches to the actuator and should be adjusted with about 10mm of free play.
That's all there is to it. Mine didn't work first time, the brake
pedal switch needed to be changed. Even though it appears to be wired
correctly the cruise version has two sets of contacts, one which
makes and one which breaks when the brakes are applied.
Also the dash warning light for the cruise control was not operative
to begin with. I found that there is a wire missing from the Orange
coming out of the cruise ECU
which should be connected to the 4th pin of the connector at the RH
side rear of the dash instrument panel. See
here for how to remove the
speedo.
A brief update to this, I've just been told that the clutch switch is not actually present on all cars (I guess I was lucky !) so this may need fitting also. Thanks to Stewart Weller for pointing this out.
Thanks to Stephen Freeman (who started this off by giving me the actuator), Anton Robinson for details of how he fitted it to his car, and finally to Graham Wharton for taking pictures of various bits of his Sterling so I could see how they fitted together and for letting me have his spare cruise ECU and slip-rings. Many thanks.
