Topic

Whilst investigating the boot light (and why it wasn’t working) I discovered that the key operated boot switch has what I believe to be a “momentary on” switch rather than a change-over switch from off to on.

My immediate thought on this was that it must be to pulse a relay and change its status but I can’t see what would re-set that status.
Can anyone please explain the purpose of that micro switch?

I am sorry but I could not follow your explanation. There is no micro-switch in the boot lock, but proper metal spring which makes contact in boot lock to provide boot light.

Thank you for the response. When I investigated this switch I had the foam cover off and noticed a thin metallic spring lever and that seemed to push on a “button” within the switch body when the key is turned.
After some further investigation I loosened the boot lock itself by removing the two bolts. That enabled me to ease the cable from the key operated switch and disconnect it. I’m not a 100% sure now as I type this but I think that “button” switch only makes contact when the key is fully turned.

In the back of the boot lock itself (the central lock that secures the boot lid in place) there appear to be two at least wires that are intended to be earth wires, one of which is itself a thin strip that comes into contact with a roller as the mechanism latches.
I could not find out what the other black wire does (the one that points vertically down) but believe it to be part of the boot light circuit itself.

Why am I investigating this - well it’s a bit embarrassing.
I was seeking a temporary supply for an instrument. The 12 volt permanent live to the boot light was perfect for my purpose.
I managed to feed a wire down the boot lid internal cavities and out through the grommet conveying the other 7(?) wires but not in that conduit.
On completion that perishing boot lamp would not work. (I had closed the lock manually to initially stop the light from working whilst I worked in the boot area- on completion and re opening the boot using the key the light failed to work)
12v to the bulb , 12v downstream of the bulb but no illumination.
Touch a spare wire to the ground side of the bulb to earth and the light works. So something in the boot lock or key operated switch was preventing a connection to ground.
Today I read that within the cavities of the boot lid there is the possibility of concealed connections on the left hand side of the lid. How on earth they would have been fitted after forming and painting the lid is a puzzle.
But all this does not explain the function of what I believe is a momentary on switch activated when turning the key.

From what you describe that should be nothing to do with the boot light, it probably to disarm the alarm system when you open the boot using the key, the alarm should re arm itself when the boot is closed again.

If the alarm is set & the boot opened by the key, the boot light would trigger the alarm, the microswitch sends an interrupt signal to the alarm control to say “Don’t panic, all is well, the key is correct & thus it must be legitimate !”
All that with just a momentary make of a contact.
M

Thank you all for the responses.
That sounds reasonable.
I suspect the earth/ground connection is dirty somewhere as the light is a lot brighter if the ground side of the bulb is taken straight to ground.

I’ve developed a number of keyless entry systems for different cars within the classic diaspora & in most cases an interrupt signal is required.
My f has an rf receiver used in parallel to the interior remote boot latch & without an interconnect to that switch circuit the device is useless.
Each design has a momentary link to ground on operation.
That momentary grounding makes the boot alarm circuit inoperative until reset.
I’ve spent a lot of time splashing around in the deep end of the MG electronics pool whilst looking at this & other items & I don’t recall a direct coronation between the switch & the boot light,
There might be secondary routes for more current to pass within the network when the microswitch is operated, but I’m unaware of it. This could be because I’ve never gone looking for it.
M

Boot light is directly operated by spring I mentioned in my post. That spring makes ground contact when boot lid is opened and breakes that ground connection when boot lid is closed. You can remove plastic black cover and you will see how it operates. This same system will trigger alarm if forced to be opened but not by the key.
Microswitch you are mentioning is used, as said, for telling 5AS alarm box that key is used to open the boot lid if alarm is set.

Take a look at this thread with pictures: https://www.mg-rover.org/threads/how-to-adjust-the-boot-light-within-the-latch-mechanism-on-200-25-zr-sw.269475/ to see how boot light switch works. It is for Rover 200 but completely the same latch mechanism is used in MG F/TF.

Top man, I’ll get the circuit diagram out later & have a look.
I’ve never been faced with a boot light problem, other than the bloody thing dropping out due to broken clips, (glue is the answer to that).
Due to my wife’s failing eyesight I have improved the boot illumination to such a degree that a pair of welding goggles are mechanically proffered for those with 20 / 20 vision, prior to the lid fully opening.
M

This is most informative and very welcome and I am extremely grateful for all the input.
I just need a bit of help with finding that switch that Roverlike identified and that operates as the boot lid opens.
I can’t see that anywhere unless it is a proximity switch and positioned over the water expansion tank that I thought might be the engine bay temperature sensor.

I identified a switch in the physical locking mechanism that is I believe operated as the boot lock catch engages with the fixed hoop at the back of the bodywork but that does not seem to match what Roverlike describes. Or am I misunderstanding?

In both following pictures switch I am talking about is circled in yellow. On first picture switch is in opened position when boot lid is closed and in second picture switch is closed when boot lid is opened.

You are looking in one place, we are referring to another.
You are literally looking at the lock mechanism & I am looking at the key hole & we are both correct in our own way, however it is semantics which has squeezed itself between us.
You referred us to another forum where a picture illustrated something which I didn’t recognise & as I was up to my eyes in recovering from a couple of weeks away I assumed my error.
It becomes clear now & I suspect Del is referring to the V4 microswitch mounted on the retaining ring of the key hole.
Is this correct now?
M