Keyswitch Disassembly

Here I take apart and reassemble the keyswitch from a Mk3 Golf. This one came from a petrol model but appears to have the same functionality as the one in my TDI.

I took this one apart because the one in my car wasnt working, resulting in bizarre radio operation due to the fact that the 'accessory enable' line was not receiving consistent 12V. Symptoms included random radio operation or (weirdly) radio on when it shouldn't be and off when it should be on.

As it transpired, this one (and probably another which I threw out) works perfectly. If you test one by plugging it into your car make sure of two things:

• You insert your key into the ignition if you have an immobiliser (or you will get a CEL flashing).
• You push the inside of the switch down when you rotate it.

If you don't push the inside of the slot in the switch in, the accessory enable line will not receive 12V.

Insert a tool (I used a knife) between the two halves of the casing where shown. Once inserted, rotate the knife along the seam and it will pop off the 'peg' that holds it secure.

Repeat this on the second lug, but *be careful* to hold the switch such that it does not suddenly spring open and shower its contents across the room.

If you are careful, it can look like this:

This image shows the top and bottom of the switch casing (the rotor is in the top section) as they come apart. It shows the correct alignment of the two switch casings and the rotor, so it is useful to refer back to this image when reassembling your switch.

Support the bottom of the rotor with your finger and push it down with a suitable object (eg. pencil) out of its casing. dont push in the centre of the slot, pus on the part the slot is moulded into (or you may end up holding several loose parts).

The removed rotor. You can see one of two springs under the copper ring in this image (center). be careful not to lose them.

The bottom half or 'contact' or 'pin' side of the switch housing.

Close up of the rotor

Remove the centre contacor ring. This carries power from the centre (30) pin of the switch. If you look closely you can see a 'dent' in the metal. This 'dent' rides on the inside of switch housing (contact side) and prevents contact occuring in certain switch positions.

Beneath it is what appears to be a spring. THIS IS NOT A SPRING. It is, in fact, a compressed coil of wire and acts as if it was a solid 'plunger'. Do not be tempted to 'unwind' it to 'restore its springyness' because it never had any to begin with.

Remove the main contactor. This 'Y' shaped piece of metal makes and breaks all the other contacts (apart from the accessory enable line) in the switch. The 'base' of the Y rides along the profile cut into the side of the bottom (contact) half of the switch casing, which lifts it from the contacts, rather than simply swiping it from one contact to the next. This presumably prevents arcing and prolongs the contact life.

Close up of the centre of the rotor. You can clearly see the two springs that the 'Y' shaped contactor rides on. Between them is the hole in which the coiled wire 'not spring' sits. Below the middle hole is a metal contact that doesn't quite meet the copper 'ring' contacts centremost element. This is the 'centre switch' that must also make contact in order to enable tther accessory 12V output from the switch. If you poke something in the slot in the rotor, you can watch the contacts move. Power flows into the copper ring and is picked up by the outermost 'wiping' contact on the switch 'bottom' (the bit with the pins on)

Watch out for this little sucker. This is the part that prevents you from restarting the engine without first returning the key to the off position. It runs in a track cut into the switch cap.

This is the spring and bronze peg that will go missing if you are not careful!

Beware of the two springs under the copper contact ring - dont lose them or let them engage themselves around the edge of the ring!

The above should be enough info for you to dismantle, diagnose and repair your keyswitch. Good luck!