The Horn/Indicator Switch - The Magnette's Chinese Puzzle?

Magnette owners who experience problems with their horn ring or indicator switch often embark on removing the offending unit from the centre of the steering wheel to investigate the fault. Few of them realise that this apparently innocent task will be the one that drives them to the edge of madness and the brink of self-harm! Seldom has a design so effectively baffled the home mechanic and seldom has a workshop manual been so devoid of the necessary guidance! But fear not: the expertise of the Z Magnette Register is here to help.

 Steering_Wheel_Centre

First a few general descriptions of the components. It is a feature of the Magnette’s design that the trafficators or indicators and the horn are all operated from the centre of the steering wheel. What is more, the decoratively badged centre  boss with the indicator switch is static when the wheel turns (as if by magic!).The indicator switch is also self-cancelling and uses the rotation of the wheel centre,  after turning, to switch the indicator off. This remarkable design feature is achieved by routing the related wiring up to the wheel centre through a static steel tube, known logically as the stator tube, that runs the entire length of the steering column. It is held in place at the bottom of the steering rack by a nut (23) and an olive (a compressible ring)(22)Steering_Column_Bottom both made of brass. The wiring passes out of the tube through the olive and nut and connects to the main loom with bullet connectors. At the top of the tube is a switch assembly (see drawing) that has a spigot that fits tight in the stator tube. The Bakelite switch unit  (88) is held in a metal cradle (90), in which it is able to turn, and the cradle anchors the assembly to the wheel. The attractive centre boss (83) carrying the MG badge is purely decorative and has no function in relation to the horn. It is simply pressed into position and held by three studs.

If the switch assembly works loose in the stator tube (93), it will start to turn with the wheel. This is disastrous because twisting strain is then applied to the wiring and it will soon break away from its connections. If this happens, there is no option but to remove the switching unit so that the connections can be remade and new wires installed if necessary.

Here is how it is done:

  1. There are many small components in the switch unit. Whether you intend to work on it in the car or on the bench, put a clean white sheet under the work so that any dropped parts can easily be seen. Garage floors will eat them up, never to be seen again.
  2. Gently spring the centre boss away from its mounting, starting at the lower edge. This will reveal the top of the switching unit.
  3. Take off the indicator switch lever (82) by removing the screw at its base (96) and pulling it off its hexagonal mounting. Do not be tempted at this stage to remove the horn ring from its three mounting studs THIS IS IMPORTANT!
  4. Using a small screwdriver, slacken the three clamp screws that are accessed through holes under the steering wheel centre. This should free up the whole cradle and switch assembly from its steering wheel housing. However, it will be held in place by the wires attached to it via the steering column.
  5. If you think the problem is minor, then it is possible to dismantle the switch inside the car and carry out basic maintenance, such as tightening loose components. However, if you know or suspect that solder connections will need to be remade  or wires replaced, you will need to withdraw the wiring completely , so the bullet connectors must be undone and the bullets unsoldered from the wire ends. The wires cannot be withdrawn with the bullets in place.
  6. At this stage the help of an assistant is desirable. While you gently pull on the horn ring, your assistant needs to be under the front of the car feeding the wires up into the brass nut on the steering rack so as to minimise damage and avoid jams.
  7. As you draw the unit upwards, the central spigot at its base will emerge from the stator tube and eventually the wires will follow. Once you have withdrawn enough length, there is enough space to access the bottom of the unit. If you are taking it right out, just continue to pull the wires through until it is completely free.
  8. It is very tempting to look at the three studs holding the horn ring and assume that they hold the assembly together. In one sense they do, but if you try to withdraw them from the top, the nuts inside the unit will become partially loose and the studs will start turning to no effect. That is when the madness starts! It is essential to release the switch unit from the cradle before you attempt to open it. Only attempt to remove the horn ring from the studs if you can securely hold the nuts underneath it to prevent the studs from turning while you undo the nuts on top. In fact the hexagons under the horn ring mounting are not nuts, they are an integral part of the stud.
  9. The switch unit is held to the cradle by three concealed screws. This is the Chinese puzzle! In order toIMG_4060Areveal them, you need to release a brass plate that covers them so that it can rotate and line up three cut-outs with the screw heads. Look carefully at the lower edge of the Bakelite switch body where it sits on a circular metal plate. There is a small cut-out in the metal plate into which has been bent a brass tag. Bend the tag down to free it from the cut-out.
  10. Looking at the bottom of the metal cradle you will see three holes. You need to line these up with three cut-outs on the edge of the brass plate that is visible through them. Then, using a small screwdriver through one of the holes, lock the brass plate in this position while you rotate the Bakelite body. Eventually you will see three small slotted screw headsIMG_4057 come into view in the cut outs. Remove these screws.
  11. As you remove the last concealed screw, the switch unit will come loose from the cradle and you can free it by withdrawing the wires through the spigot.With the switch unit free, you will see the wiring connections under it. There is one separate  wire connected to a brass stud. Three other wires are connected to a small segment-shaped paxolin panel that is held in place by two more nuts on studs. You will see that these three studs are the same ones that pass right through the unit and hold its metal top in place. Wire colours may vary but the original wiring diagram gives: Horn – brown, indictors – green, light green and dark green. To add confusion, these colours are not the same as the ones to which they connect via bullet connectors to the main wiring loom. See wiring diagram.IMG_4056
  12. Now that you can access both ends of the studs, you can undo the nuts (each of which has a brass washer and a shake-proof washer). As you withdraw the studs, take care because the two Bakelite halves will separate and there are sprung parts inside that may disappear into the wide blue yonder. For ultimate security, take it apart inside an old pillow-case.
  13. Once the two halves are separated, the wiring will come away completely and you will see that the other side of the paxolin panel has three brass contacts that push into matching holes in the body. Inside the switch is a rotating plastic moulded arm with a pivot that sits in a hole in the body. At the bottom of the arm is a tiny sprung wheel that bears on mouldings in the body so that the arm firmly locates in the three indicator positions corresponding to right-off-left. Under the arm is a tiny brass contact plate that rides on the three brass contacts and is held against themIMG_4047 by a tiny spring located in a hole underneath it. It is these tiny components that will go astray if you do not keep them under tight control. The arm also locates between two springs that move on a curved wire, so that it will return to the off position in the centre. Next to the arm on each side is a hinged pawl that actuates the self-cancelling mechanism. Pay careful attention to the location of all these parts.
  14. At this point dis-assembly is complete. Carry out whatever repair is needed before reassembly. A small quantity of suitable grease is applied inside the switch to lubricate theIMG_4035contacts.
  15. Re-assembly of the switch unit is fiddly and because the compression of the sprung components is involved, you are well advised to use the pillow-case again. It may take several attempts to get everything in place. I suspect that Lucas selectively bred a race of six-fingered mutants to carry out this operation.
  16. Once the two halves of the body are re-united and the three brass studs are in place, the switch can be re-attached to the cradle with the concealed screws. Then the brass plate is rotated back over them so that the locking tag can be bent back into place.IMG_4043
  17. Before the unit is replaced in the steering wheel, it is a good idea to test the electrical connections for continuity, especially the horn ring contact, which is expected to work at various angles to allow the horn to be operated by either hand in various positions.
  18. Feeding the wires back down the stator tube can be a fiddle. Attach a draw string securely and cover the wire ends to keep them neat. Heat-shrink tubing can be effective as long as it will fit in the tube. Lubricate the wires with Vaseline or similar to aid their progress down the tube.
  19. Make sure the wire ends are clean before attempting to re-solder the connector bullets.
  20. Remake all connections and test the horn and indicators with the steering wheel in various positions.
  21. Have a beer: you deserve it.

Addendum (March 2013)

Steve Hanegan has kindly uploaded a picture gallery of the various steps involved in dismantling the horn/indicator and stator tube. Click HERE to view it. Once it is open, roll your cursor over each photo to see the full caption.

Comments  

#1 Geoff Bennett 2018-07-19 19:59
Hi Steve. Brilliant work! As you know this unit is very similar to that of Wolseley 15/50 . Do you know anyone who can refurbish one of these units?
I can't find it in the 1957 list of Lucas parts, maybe it was made by someone else.
Best wishes
Geoff Bennett Wolseley Register 4/44, 15/50 adviser

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