This £149.95 cruise control from www.Conrad-Anderson.co.uk is their budget vacuum operated model. Other models feature stalk & infra red steering wheel rim mounted control as well as speed memories. Delivery was free and it was received within 3 days of ordering by phone.

1) The command module with on/off, set, resume, accelerate/decelerate buttons is designed for dash mounting.

However, after disassembling it, I discovered that it would operate fully, with only 3 of the 4 wires connected. The fourth wire only drives the 'on' led so I fitted this to the dash next to the mirror controls.

The photos show the spare positions in the wheel boss connector and mating connector under the column cowl. I just pushed the bared ends into the connectors, as I had none of the correct terminals - it is working fine so far though a drop of glue might not go amiss.

The command module was then mounted on the underside of the wheel with the double sided tape provided as the photo shows, so it literally gives finger tip control.

This works even better than stalk or boss mounted controls. There was already a 7mm hole in the underside of the boss through which the cable to the command module was routed.

2) The cruise control is designed to use 2 or 3 magnets fixed to the inner CV joint with a large cable tie to sense vehicle speed. This works fine but is prone to reliability problems as the cable tie can work loose. Not to mention being extremely awkward to fit.

Fortunately, Rovers have an electronic speed transducer fitted to the diff housing. This, I found, produces 10,000 pulses for every mile travelled. To interface this to the ZT50, required 1 transistor and 2, 10k ohm resistors. I just soldered it together and encapsulated it in heatshrink sleeving, with the 3 wires scotch locked to the transducer wiring and the 4th connecting to the ZT50 speed input. See below for circuit.

The fitting instructions are adequate and a comprehensive collection of bits & pieces for mounting & connecting it is supplied.

The photo shows the vacuum servo mounted on the bulkhead - it faces away from the throttle potentiometer (TPS) as the cable is longer than needed but cannot be shortened.

The vacuum pipe tees off the pipe to the EGR solenoid. Various sizes of tees are provided.

The cable loops around and pulls a lever fitted to the TPS as can be seen.

There is a handy slotted mounting hole already drilled in the TPS bracket (for LH drive cars)

A reed switch and magnet should have supplied which is fitted to the clutch pedal. This prevents the engine over-revving if the clutch is pressed whilst the cruise control is engaged. It was missing from my kit, so I made a bracket to hold a v3 microswitch as shown, connected as per the instructions.

A connection is also made to the brake pedal switch so that pressing either this or the clutch disengages the cruise control.

 The control module was slid down the right hand side of the centre console side panel - just behind the heater outlets.

I initially started off with the sensitivity set to the 'high' postion. This worked fine but was a bit too abrupt at adjusting speed, so I set it to the middle position. The ZT50 held the speed to within plus or minus 1mph uphill or down dale with smooth, barely perceptible adjustments.

I then gave it an unfair test - 30mph in 5th (1100rpm!) up a 12% incline. It actually managed it - not that I normally labour the engine to that extent! (I'll bet there aren't many L series' that will pull 1100rpm in 5th on the level, never mind up a 12% hill - but that's my MAFAM & Superchips remap at work!)

Just been for another spin & have found, that due to the location of the controls, I can use it as a hand throttle, using the acc/dec buttons to adjust my speed.

My next project is to interface the sat nav to the steering wheel so the car steers itself as well, then I can have a snooze.....!

 

The circuit to interface the Rovers speed transducer to the ZT50.

The car's transducer signal is a 12volt pulse, at 10,000pulses per mile.

The ZT50 instructions says it will work with either 2500, or by cutting a wire loop, 5000ppm but it works fine with 10,000.

Maplin part nos:

BC517 = N52AH; 10K RESISTOR=M10K; DIODE =QL73Q