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Waeco MS-50 Cruise Control

Upgrade Guide Waeco MS-50 Cruise Control

As I understand this cruise control can be hard to get hold of in the UK but you can buy one on https://www.ebay.co.uk (search for 'waeco ms-50') and import it from Germany. You can find info from the manufacturer on https://www.dometic.com/ and also download the installation manual there. Note the prerequisites mentioned: 12 V vehicle electrics, mechanical throttle linkage, vacuum power source.


I mainly address those issues specific for using the MS-50 in a Defender, all general information should be read from the Waeco manual. So please read that manual first!

Step 0: Opening the box

The cruise control is delivered with all the material needed to install it. There are three main components:
  1. The square box is the central electronic unit and can be stacked away out of sight somewhere,
  2. The small round object is the control unit, this unit should obviously be somewhere placed in sight and reach of the driver,
  3. The blue object is the vacuum powered servo unit which controls your throttle with a Bowden cable. In my Defender case this unit is placed in the engine compartment.
Both 2 and 3 are connected to the electronic unit with the supplied multi wired cables.

There are three more connections made to the electronic unit:
  1. The power supply, 12V switched, 12V permanent and ground.
  2. A single wire for detection of engaging the brake or the clutch pedal. The cruise control switches off if either of these pedals is used as a good cruise control should do.
  3. A double wire going to a pick up coil which detects the revolutions of the drive shaft. In my Defender case I used the shaft going to the back wheels, simply because there was not much room installing it near the shaft driving the front wheels.
Step 1: Installing the central electronic unit and power supply

I have chosen to wedge it behind the wiper motor, it is relatively dry there and the 12V switched and permanent connections can be easily picked of from the wires leading to the interior light and hazard light switches mounted on the dashboard panel which has to be removed to be able to reach the wiper motor. Use a multimeter to find a permanent live wire and a wire which only has 12V when the starter key is turned. The ground connection I picked up from the screw holding the box in place, see picture. Just below the box a 10mm hole should be drilled to the engine compartment. Nearly all cables going to the electronic unit will pass through this hole.


Don't mind the second wire under the screw on the picture, the blue one has another purpose. In your case only the green wire is there.

Downside of this location is that the little diagnostic LED mounted on the bottom of the box near the connector is not really visible when driving. But in the end I didn't need this feature anyway.

Step 2: Installing the brake and clutch pedal detection

Check the wire diagram in the Waeco installation manual also!

The brown wire leaving the electronic unit used for that is first connected to the clutch pedal reed switch which is glued just above the clutch pedal, see picture. A small hole is drilled near the pedal, the brown wire is leaded from the electronic unit through its 10 mm hole, through the engine compartment and then again back into the passenger compartment through the little hole near the clutch pedal. So no wires are running in sight over the inside bulkhead (which could be an option of course). The magnet used to activate the reed switch is glued on the pedal itself. If the pedal is not touched the magnet activates the reed switch, if pressed the magnet moves away from the reed switch and deactivates it. You can simply check this by using a multimeter to measure the resistance over the reed switch. When the pedal is up the the reed switch is activated which means it is closed so it has a near zero resistance. When the pedal is pressed the reed switch opens and the resistance should be infinite.


The second brown wire leaving the the reed switch is going back through the small hole near the clutch pedal and is lead to the car brake pedal switch. I used heatshrink sleeving so it looks as if only one black cable is going through the hole but in fact it contains the two brown wires of the reed switch. The brake switch on my Defender is located on the back of the pedal box housing in the engine compartment almost against the bulkhead. Use a multimeter to check which wire to use, that is, which wire becomes live with 12V when the brake pedal is pressed and the brake lights are on.

Important: I learned this the hard way: If you use LED lights for brake lights the electronic unit will think that your brake lights are gone because of the high resistance of a LED light compared to a normal bulb light and will therefore not activate your cruise control when you request it to do so.

Step 3: Install the control unit

I glued the control unit on top of my dash, see picture the wire is leaded behind the dash clocks down to the electronic unit.


Step 4: Checking the connections made so far

Use the Waeco manual to perform the 'Test A'. That's when I learned that LED brake lights won't work and that I had picked a wrong wire for the 12V permanent.

Step 5: Installing the drive shaft rotation speed sensor

I installed the sensor near the rear shaft but when you feel lucky you can try to do it on the front shaft. Advantage of that will be that you will not need to extend the supplied black/blue cable. In my case I had to because the rear shaft was to far away from the electronic unit. Solder the wires and use heatshrink sleeving to protect the connection when you extend the wires. Note that the gap between the magnet tied to the shaft and the pick up coil must be 3 to 5 mm. After installation mine was spot on, 4 mm gap.


Note that when trying to find a good location for the pick up coil the drive shaft can be moving up and down quite a bit when off roading so I guess it is better to pick it up from the side.

Measuring the working of the pick up coil with a multimeter is not simple. It is not a reed switch as used with the clutch pedal so you can't measure its resistance to check if it is working. In fact the rotating magnetic field of the magnet passing the pick up coil will generate a little current spike which is picked up by the electronic unit, the higher the speed of the magnet the higher the pulse. So when the shaft and magnet are static there will be no current generated in the coil. The only thing you can check with a multimeter is that the resistance of the coil should not be infinite (broken wire) nor must it be zero (short circuit between wires). Note that in my case I had to attach two magnets (there are three in the package) to the drive shaft, opposite of each other to minimize imbalance. The reason for this is explained in the last section. Note also that Waeco states that the minimum drive shaft diameter should be 60 mm, and yes in my case the drive shaft diameter is 50 mm. Implications of this are also mentioned in the last chapter.

Step 6: Installing the servo unit

The servo unit is bolted on the bulkhead. Note that the metal bracket on the unit can be removed, turned and attached again to make it a mirror image which could help finding a good spot to mount it on.


The Bowden cable is piggy backed on the existing throttle cable. I have an Edelbrock carburetor so when using another carburetor you have to experiment a bit to find the right way to attach it.


The travel of the vacuum servo Bowden cable is 40 mm and should match the travel of the point of the carburetor attachment point to which it is attached. In my case the travel of the original throttle cable was also 40 mm so hurray.


The vacuum is taken –in my case- from the LT95 diff lock vacuum tube, but you can use any vacuum source. Tubing and T pieces in several sizes are included.

Step 7: Checking the connections made so far

Use the Waeco manual to perform the 'Test B', checking the working of the servo unit. That's when I learned that mimicking a bulb brake lights with a 1000 Ohm resistor parallel to the LED brake light does work for test A but not for test B. So I switched back to good old glass bulbs for now.

Step 8: Running test, configuration

All has been tested so far with test A and B except for the workings of the pick up coil. So time for a test drive! And as you might have guessed when pressing the 'Set' on the control unit nothing happened in my case. When measuring and checking everything again and again I remembered a little switch on the electronic unit which determines the sensitivity of the pick up coil, it will be in 'Normal' as a default. Well, I needed to set it to high. Maybe because I had the extend the pick-up coil wires but probably because my drive shaft had only a 50 mm diameter, where 60 mm was the required minimum. This reduces the speed with which the magnet travels passed the coil making the current spikes smaller than normal. So pick-up coil sensitivity switch set to 'High' and test drive again! Now the cruise control was working but only at a speed range of 30 – 80 km/h. In the Waeco manual it is mentioned that when this happens you have to cut a black wire running in a loop from the electronic unit to alter the number of pulses internally in the electronic unit. Ok, cut the wire, third test run: now the unit was only working with speeds over 120 km/h at which speed the gurgling noise of the fuel leaving my fuel tank is louder than the sound of my V8. After some thought and reading the manual again the solution was simple, double the number of magnets on the drive shaft, I had used only one which is standard so I added a second one. That will give twice as many pulses and that will have the electronic unit thinking that I am still driving 120 km/h when in fact I am driving 60 km/h. And yes, that did the trick, I am now the happy owner of a working cruise control in my 1983 OneTen.

So in short:
  • Do not use LED brake lights
  • Set the sensitivy switch on the electronic module to 'High'
  • Cut the black loop wire on the electronic unit
  • Use 2 magnets on the drive shaft
Good luck!
Arthur II
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