Warning Light

[Guest Fred2b]

I have found in my box of tricks a small flashing red LED that is supposed to simulate an active car alarm ( I think I bought it from Maplin a few years ago for about £2 ) but never got round to fitting it to my Golf.

It needs to be connected to a circuit that is live with ignition off but dead when the ignition is on. Anyone know any such circuit and wire colours please.

I know it's not the same as an immobiliser ( which I now have fitted to the battery using one of those black screw in knobs) but maybe a visual indicator will add that extra bit of doubt to the low life scroat thinking of having my car for a joyride!!

Pete

[Guest Ant]

I don't think there's a live from the ignition switch when it's off, but I think I'm right in saying that the wires which are live when it's on go to ground when its off ... so ...

 

solution 1 - Put the led circuit between a permanent 12v and the ignition switch output. With the ignition on it has 12v both sides and won't light up. When it's off it will have 12v one side and 0v the other so it will light up. You need to test that I'm right about this with a volt meter first. The indicator switch definitely behaves like this (which is how one dash warning light covers both left and right but not hazard) but I'm not definite about the ignition switch.

 

solution 2 - If that doesn't work then get a "single pole dual throw" relay. This has the coil connections and then one input and two outputs. The input is connected to one of the outputs when the coil is not energised and to the other output when the coil is energised. Connect the relay coil to a 12v ignition wire and the other side to ground. The relay will click when the ignition is switched on and off. Put a permanent 12v on the input pin, and connect the "normally closed" output to the LED. The other side of the LED goes to ground. The "normally open" connection on the relay doesn't go anywhere. With the ignition off the 12v flows through the relays "normally closed" output , through the diode and to ground. With the ignition on the relay coil is energised which breaks the 12v from the LED circuit. The relay will be active whenever the ignition is on, just like a fuel cut-off valve is on carbed cars.

 

Ant

 

PS - A single pole single throw relay would also work for solution 2 but it needs to have normally closed contacts, not normally open.

 

PPS - Yes Bill ... it's another long post. How's the battery going on?

[Guest Mr Pid]

A less technical solution would be just leave in a permanent feed from the battery with a switch to turn it on and off when you want!

 

Personally i would go for Ant's idea as it sounds clever and leaves little room for forgetting to switch it on!

 

Stu

[Guest Bernie]

I agree that Ant's suggestion of connecting between a the battery +ve and the IGN swithed positive should work. I don't thing the IGN switched positive actually switches to ground in the off position but the resistance of the circuits on that supply will be low enough to drive the LED.

 

As an alternative you could always pick up on either the brake warning or oil pressure warning lines. These are switched to ground with handbrake on or low oil pressure, i.e. not switched to ground under normal driving conditions.

[Guest Battery Bill]

Ant

PPS - Yes Bill ... it's another long post. How's the battery going on?

Very well thanks, Box fitted permanently tonight but we are not alowed to talk about it any more sorry . :boohoo: :boohoo:

[Big Jim]

With reference to the LED (That was what the thread was about after all!)

 

run a feed directly from any perminantly live connection to one side of the LED (note that the LED will only work one way) then connect the other wire from the LED to 2nd position on the ignition switch (or any feed wire when the ignition is on)

 

This means that the LED is live when the ignition is off, by grounding the minute current of the LED through the other electrical appliances when they're not powered up, but once the ignition is switched on, feed is then on both terminals of the LED so it goes off.

 

But as far as I know, only 3 Robin Hoods have ever been stolen (and that was by joy riders)

[Guest Guy]

Dont forget to stick a 680 ohm dropper resistor in seres with it.

[Big Jim]

most (if not all) flashing LED's have a resistor built in them.

[Guest Fred2b]

Thanks guys I will try to fit it tonight. Since I bought it from Maplin as a flashing LED I will assume it has a resistor fitted.

Pete