nokia 7210 handsfree connection

[ringworm]

I have a car kit for the 7210 but when i plug the phone in it comes up that
it is connected to a headset (hence the keypad lights go out after a minute
or so) On inspection i found a 4k7 resistor across two of the connections in
the car kit, i remember reading somewhere that on an earlier model the phone
tells what type of device it is connected to by the resitor in the device.
does any one know if this is correct and how i can get the phone to think it
is connected to a car kit.

Many thanks

Jon