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MG MGF Technical - Flashing LED - How to wire up? (No MG content)

Another non MG related thread - but it is car related!
I would like to wire up a led to my motorbike so that it illuminates when the ignition is switched off, but extinguished with the ignition on. I don't really want to use a manual switch, I would prefer it to be automatic.
Is there an electronics whizz out there who can help me?
Cheers,
Jason H
Jason H

you can buy a flashing LED spoof alarm just for this with fitting instruction,about for £1.99.

They come with 3 wires
green/blue wire connect to +12 volts

red/white wire to earth

black wire to +12 volts when ignition is on.
Joe

Joe,
Where are these for sale, I have one from Maplins, but it just has the standard 2 wires!
Jason H
Jason H

Try car accessory shops,have you a Wilkinsons hardware store I think I've seen them selling these.

As said called Flashing LED spoof alarm.

Capri club international tel may be 01527 502066 sold these but their price was £3.50.

This is what you want as only lights up when ignition is switched off.
Joe

OK, you need an LED and a suitable current limiting resistor and three wires.

wire the led so the long leg (+ve) is connetced to a wire and the short leg to a wire and the resistor, also connect the resistor to the final wire.
to connect up: wire the LED only wire to the battery, wire the LED and resistor wire to the ignition and wire the resistor only wire to the ground.
You will need a 'normal' LED, not one with a fancy resistor (marketed as 12 or 5 volt led's).
You will need to know the forward current of the LED (specs in the maplin book)
and use the R=V/I rule where V = 12 volts (or 6 for a motorbike?) and I is the forward current (usually in the order of 5 or so milliamps).

So for 5 millamps and 12 volts you should need a 2400ohm or 2.4kohm resistor, 2.4kohm resistors don't exist so go for the next value up.

A Quarter watt resistor shouldl be ample for the current used.
Will Munns

Will

Most modern bikes are 12 volts - but, due to space availability, with very small batteries - so what ever Jason fits it must have the absolute minimum drain effect or he will soon suffer flat batteries - or do as I do and plug in a battery minder when ever possible.

Ted
Ted Newman

The drain will be the forward current of the LED, flashing LED's use more current as do brighter ones and non red ones. But dimmer ones will be more difficult to see in the sunshine when outside.
This system will continuely use the same amount of current wheather or not the ignition is on.

Will
Will Munns

Battery drain is the reason I have removed the alarm, I must admit that the prewired option for £1.99 sounds the easiest, as I know virtually nothing about electronics and I would be really worried about the diy option using resistors etc.
I still have the nice 12v led fitted in the fairing from the previous alrm installation, but it sounds as though I will not be able to reuse this!
Cheers,
Jason H
Jason H

Jason

I have a garage so am able to make use of the battery minder option to keep the power up - but a friend has a Ducati and no garage and is paranoid (rightly so) about having the bike nicked so he now has two batteries, one on the bike and one off the bike being kept up to charge and he swaps them every weekend and this has worked well for him for at least two years to my knowledge.

Ted
Ted Newman

Jason,

As I read it you require the LED to illuminate only when the ignition is OFF, so wire the LED and resistor across the ignition switch. The positive side of the LED to the battery side of the switch (assuming negative earth) and the negtive side of the LED to the switched supply side.

You can buy LEDs with the resistor built in from car accessory shops.

HTH

Bruce
Bruce Caldwell

Bruce,
That sounds far too simple!
If I wire it up as you suggest then would the electricity just go via the led and power whatever circuit I have connected it to, effectively bypassing the ignition?
Jason H
Jason H

No. The current through the LED is only thousandths of an ampere. The current required to power the other circuits is in the region of amps each. The current thorough the LED would also pass through the other circuits but it would not be enough to make them work. Try it!

Bruce
Bruce Caldwell

Yes it should work, but as you say it will pass some (albeit small) current to the rest of the system, this should not be a problem unless you have any computerized systems in the bike (ecu etc). If you have then it might prove to be a big no no.

Will
Will Munns

Thanks for the advice, I am tempted to put it on a live and a switched live as Bruce has said, but am worried about damaging any components, so have ordered one of the 3 wire leds from the capri club.
It should be easier for me to fit as well, as I won't need to find a switched live which has no other switch in the circuit, as the obvious switched lives such as headlights or heated grips have other switches in the circuit which would need to be "on" for the led to work (or so I think!).
I'll let you know if the 3 wire capri led doesn't work!
Cheers,
Jason H
Jason H

Now to put a bit of MGF content into the thread.

I have been considering removing the inner door lock poppers on top of the door facia and replacing them with flashing LEDs as I have not found a use for these. If you do require to lock yourself in the car you can use the Blipper. I hope this makes sense, anyway would these Capri kits be of any use for this purpose, they would solely be a visual deterrent like the dashboard LED but on each of the car doors. What does every one think?
Chris

<<If you do require to lock yourself in the car you can use the Blipper>>

If you lock yourself in with the blipper the alarm will go off when you move about in the car. It takes 30 seconds or so to arm, and then you'll have to keep very still! The plungers are the only way of locking the doors while on the move. The blipper is useless of course when the engine is running.

Occasionally it is comforting to be able to lock oneself in when driving in slow moving traffic in a potentially hostile area. Especially if you are a female.

I would investigate combining the LEDs onto the plungers so that you get the best of both worlds.

Bruce

Bruce Caldwell

Good thinking Bruce, back to the drawing board I suppose.

regards
Chris
Chris

Bruce,
Whilst I was looking for my led I did come across some replacement door lock pins with leds set in the top - not sure if they would fit the F though!
Jason H
Jason H

Where did you see those pins Jason?

Bruce
Bruce Caldwell

Try www.richbrook.co.uk

Also Demontweeks.
Joe

Bruce,
The ones I saw were similar to the richbrook items, although they had a red led in the top.
I saw them in my local "Max Power" type car accessory shop!
Jason H
Jason H

This thread was discussed between 23/09/2002 and 30/09/2002

MG MGF Technical index

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