Security LED

[chrisanthony]

Hi everyone

I just purchased a LED Varad Scanner. Is there a way to hook it up behind my radio so it can only come on when the engine is off?. It has 3 wires 12V(constant)/ground and yellow. I have it hooked up on the constant radio wire for now, but very distracting when driving at nite.

Thanks.

Chris
96 escort lx

[Selectron]

I'd guess that the yellow wire might be for that purpose, so I assume you didn't get installation instructions with it. If there's a model number on it, it might be worth checking the Varad website and see if the instructions are available there.

If you have to do it with two leads though, it can be done. You could use a relay, and wire it such that the contacts would be held open while the ignition is switched on, closing when the ignition switches off, thereby completing the circuit automatically. You would just route either the 12V wire or the ground wire via the relay's normally-closed switched contacts. That's kind of a clumsy solution though.

If the unit is intended to be operational when the ignition is switched off then it presumably doesn't draw much current. If that's the case then there's a neat way to wire it, by connecting the 12V wire to a constant 12V feed, but then instead of connecting the ground wire to ground, connect it instead to the top end (the 12V end) of a relay coil, but it must be one which is fed with 12V any time the ignition is in Start or Run - you don't have to add that relay - I'm talking about one of the relays already fitted in the car. When the ignition is switched on, the 12V wire would then have 12V, and the ground wire would also be sitting at 12V (because it's at the top end of the relay coil) so there would be 0V potential difference between the two wires and thus the unit would be switched off. Then when you switch the ignition off, the top end of the relay coil would fall from 12V to 0V and would effectively become a ground point, and the unit would automatically switch on. It wouldn't be a true ground because you would have the relay's coil resistance in series, but for a low current device that isn't necessarily a problem; it depends on the unit's current consumption, and the resistance of the relay coil.

I'm on a new computer and I don't have all my programs installed yet so I can't see my wiring diagrams for your model, but when I get that sorted in the next day or two I'll take a look at them, and I'll sketch a couple of diagrams for those two methods, which will be easier to follow than the written explanation.

[12Ounce]

Clever! It might be wise to install a diode in the original coil 12v circuit ... to eliminate possible back-feed. Depends on nature of circuit.

[chrisanthony]

Originally Posted by Selectron

I'd guess that the yellow wire might be for that purpose, so I assume you didn't get installation instructions with it. If there's a model number on it, it might be worth checking the Varad website and see if the instructions are available there.

If you have to do it with two leads though, it can be done. You could use a relay, and wire it such that the contacts would be held open while the ignition is switched on, closing when the ignition switches off, thereby completing the circuit automatically. You would just route either the 12V wire or the ground wire via the relay's normally-closed switched contacts. That's kind of a clumsy solution though.

If the unit is intended to be operational when the ignition is switched off then it presumably doesn't draw much current. If that's the case then there's a neat way to wire it, by connecting the 12V wire to a constant 12V feed, but then instead of connecting the ground wire to ground, connect it instead to the top end (the 12V end) of a relay coil, but it must be one which is fed with 12V any time the ignition is in Start or Run - you don't have to add that relay - I'm talking about one of the relays already fitted in the car. When the ignition is switched on, the 12V wire would then have 12V, and the ground wire would also be sitting at 12V (because it's at the top end of the relay coil) so there would be 0V potential difference between the two wires and thus the unit would be switched off. Then when you switch the ignition off, the top end of the relay coil would fall from 12V to 0V and would effectively become a ground point, and the unit would automatically switch on. It wouldn't be a true ground because you would have the relay's coil resistance in series, but for a low current device that isn't necessarily a problem; it depends on the unit's current consumption, and the resistance of the relay coil.

I'm on a new computer and I don't have all my programs installed yet so I can't see my wiring diagrams for your model, but when I get that sorted in the next day or two I'll take a look at them, and I'll sketch a couple of diagrams for those two methods, which will be easier to follow than the written explanation.

Hi man thanks...i couldn’t find any instructions but I’ll try hooking the yellow wire up..to the black ground wire from the stereo. The steps you mentioned is this all concentrated on the ignition in the steering column? The electrical system is pretty new to me..i really don’t want to mess anything up.. I'm pretty comfortable with the radio electrical cuz if anything goes wrong i can just change the fuse.

[Selectron]

Thanks 12Ounce, a blocking diode might indeed be a smart idea; I hadn't thought of it yet.

Originally Posted by chrisanthony

Hi man thanks...i couldn’t find any instructions but I’ll try hooking the yellow wire up..to the black ground wire from the stereo. The steps you mentioned is this all concentrated on the ignition in the steering column? The electrical system is pretty new to me..i really don’t want to mess anything up.. I'm pretty comfortable with the radio electrical cuz if anything goes wrong i can just change the fuse.

No, don't connect it to the radio's ground wire, because that's always at ground potential regardless of whether the ignition is switched on or off, so it won't achieve anything and it certainly won't make the unit switch automatically. I imagine that yellow wire might be intended to hook into the alarm system, so the unit would switch on automatically when the alarm system is armed.

I got my computer all finished so I can take a look at the wiring diagrams later. Oh yes, one other option would be simply to wire it via a switch, maybe a hidden one, and just switch it on manually when you park the car. I'll see if I can find an easy automatic switching solution in the area of the radio though.

[chrisanthony]

hey..i was just thinking how bout the ignation wire going in to the radio?..could i tap into that?..but then again it only goes live when the key is turned...

[Selectron]

I'm just reading this pdf file on the Varad website. They are referring to the third wire as orange, but aside from that does it look like those instructions might refer to your unit?

Reason why I ask is, it says the unit is programmable, to select the flash sequence and the speed. It also says that if the 12V wire loses contact even momentarily, it will lose its memory and you'll need to go through the set-up sequence again. Same thing would apply if the ground connection was momentarily interrupted.

That means you can't wire it in via a switch, nor via a relay, nor can you use the ground-via-relay coil idea which I mentioned because in all cases the memory settings would be lost each time it was switched off.

Therefore it would need to have a constant 12V feed and a constant ground connection, with on/off control being achieved via the third wire. The unit is active when the third wire is grounded, and inactive when it isn't - well, that's the case for the units in that pdf.

Unfortunately, there's one detail which they've omitted, which is whether it's permissible to allow the third wire to toggle between 12V and 0V, or whether it may only toggle between an open-circuit condition, and 0V.

If the former, then that's easy to do by using the ground-via-relay coil arrangement, and I doubt the relay coil resistance would even be an issue. If it must be the latter though, then for automatic switching, that would require that you add a single-pole, double-throw (SPDT) relay, wired such that the third wire would be held in the open-circuit condition when the ignition is switched on, and then grounding via the relay's normally-closed contacts when the ignition is switched off. That's simple to do, and I can draw a sketch of how to do it, so you'll be able to do that without any problems. Or of course you could feed that wire to ground via a switch for manual switching.

I think we need to find out more about that third wire before we can proceed though. Is your unit similar to those on the pdf, or do you have a model number for it?

[chrisanthony]

Originally Posted by Selectron

I'm just reading this pdf file on the Varad website. They are referring to the third wire as orange, but aside from that does it look like those instructions might refer to your unit?

Reason why I ask is, it says the unit is programmable, to select the flash sequence and the speed. It also says that if the 12V wire loses contact even momentarily, it will lose its memory and you'll need to go through the set-up sequence again. Same thing would apply if the ground connection was momentarily interrupted.

That means you can't wire it in via a switch, nor via a relay, nor can you use the ground-via-relay coil idea which I mentioned because in all cases the memory settings would be lost each time it was switched off.

Therefore it would need to have a constant 12V feed and a constant ground connection, with on/off control being achieved via the third wire. The unit is active when the third wire is grounded, and inactive when it isn't - well, that's the case for the units in that pdf.

Unfortunately, there's one detail which they've omitted, which is whether it's permissible to allow the third wire to toggle between 12V and 0V, or whether it may only toggle between an open-circuit condition, and 0V.

If the former, then that's easy to do by using the ground-via-relay coil arrangement, and I doubt the relay coil resistance would even be an issue. If it must be the latter though, then for automatic switching, that would require that you add a single-pole, double-throw (SPDT) relay, wired such that the third wire would be held in the open-circuit condition when the ignition is switched on, and then grounding via the relay's normally-closed contacts when the ignition is switched off. That's simple to do, and I can draw a sketch of how to do it, so you'll be able to do that without any problems. Or of course you could feed that wire to ground via a switch for manual switching.

I think we need to find out more about that third wire before we can proceed though. Is your unit similar to those on the pdf, or do you have a model number for it?

Hi selection thanks for the reply..yea its exactly the same except mine isn't programmable so i'm not worried there and the yellow wire is exactly what the orange wire states in the pdf. Also when they say "Ignition - Ground when engine is “OFF”.
(See fuse box)" what does that mean? where would i hook it up to the fuse box?

[Selectron]

Can I just check something? You have the red wire connected to a constant 12V, and the black wire to ground, and the yellow wire isn't connected to anything but the scanner works when it's wired up that way, yes? Works fine aside from the fact that it doesn't automatically switch off of course - is that correct?

[Selectron]

I'll assume that my last post above is correct - if so then that means the scanner is working without having the third wire grounded! I think that instruction sheet is badly worded - it isn't so much that the scanner will switch on when the third wire is grounded, but rather it will switch on in the absence of 12V, so it doesn't matter if it's grounded or left floating (open-circuit) - just so long as 12V is no longer present, the scanner will switch on.

That means you can do all your wiring at the back of the radio, because you have a constant 12V feed there, and a switched 12V feed (hot only in Acc or Run) and a ground wire. So your red wire goes to constant 12V, yellow wire to switched 12V, and black wire to ground. No need for extra fuses, because you have the two radio fuses already in-circuit.

You might want to prove that to yourself before wiring it all up - touch the red wire to 12V, black wire to ground - the unit will work - then touch the yellow wire to 12V, and the unit will switch off. Remove the yellow wire from 12V and it will switch on again.

So when you've done the installation, the scanner will be off when the ignition is at Acc or Run, and will switch on automatically when the ignition is switched off.

You'll find that the scanner will light up briefly while you are cranking the engine - the radio always switches off for a second or two during cranking, eh, so that means the scanner will switch on during that same brief period.

If you're sitting parked in the car with the engine off, then to save the LEDs from giving you a migraine, just set the ignition switch to Acc, and the scanner will switch off.

I reckon that's all there is to it. You probably know the radio wire colours, but if not then here they are. I don't have wiring diagrams for the '96, but these are the wire colours for the '95 and the '97. One time when you mentioned wire colours for some problem or other, I noticed that those which you mentioned fitted in with the '97 rather than the '95.


1995 Escort radio power feeds:

Constant 12v - dark blue/red via the 'Room' fuse
Switched 12v - dark blue/black via the 'Radio' fuse


1997 Escort radio power feeds:

Constant 12v - blue/red via the 'Room' fuse
Switched 12v - blue/black via the 'Mirror' fuse

[chrisanthony]

Originally Posted by Selectron

Can I just check something? You have the red wire connected to a constant 12V, and the black wire to ground, and the yellow wire isn't connected to anything but the scanner works when it's wired up that way, yes? Works fine aside from the fact that it doesn't automatically switch off of course - is that correct?

yes you are correct..that's exactly how i have it hooked up rite now...after i got home i saw the top led melted i assume that's due to directly being in the sun all day..what do u think?

[chrisanthony]

Originally Posted by Selectron

I'll assume that my last post above is correct - if so then that means the scanner is working without having the third wire grounded! I think that instruction sheet is badly worded - it isn't so much that the scanner will switch on when the third wire is grounded, but rather it will switch on in the absence of 12V, so it doesn't matter if it's grounded or left floating (open-circuit) - just so long as 12V is no longer present, the scanner will switch on.

That means you can do all your wiring at the back of the radio, because you have a constant 12V feed there, and a switched 12V feed (hot only in Acc or Run) and a ground wire. So your red wire goes to constant 12V, yellow wire to switched 12V, and black wire to ground. No need for extra fuses, because you have the two radio fuses already in-circuit.

You might want to prove that to yourself before wiring it all up - touch the red wire to 12V, black wire to ground - the unit will work - then touch the yellow wire to 12V, and the unit will switch off. Remove the yellow wire from 12V and it will switch on again.

So when you've done the installation, the scanner will be off when the ignition is at Acc or Run, and will switch on automatically when the ignition is switched off.

You'll find that the scanner will light up briefly while you are cranking the engine - the radio always switches off for a second or two during cranking, eh, so that means the scanner will switch on during that same brief period.

If you're sitting parked in the car with the engine off, then to save the LEDs from giving you a migraine, just set the ignition switch to Acc, and the scanner will switch off.

I reckon that's all there is to it. You probably know the radio wire colours, but if not then here they are. I don't have wiring diagrams for the '96, but these are the wire colours for the '95 and the '97. One time when you mentioned wire colours for some problem or other, I noticed that those which you mentioned fitted in with the '97 rather than the '95.


1995 Escort radio power feeds:

Constant 12v - dark blue/red via the 'Room' fuse
Switched 12v - dark blue/black via the 'Radio' fuse


1997 Escort radio power feeds:

Constant 12v - blue/red via the 'Room' fuse
Switched 12v - blue/black via the 'Mirror' fuse

I'm not exactly clear on this..what do u mean buy room and radio fuse..its through the fuse box? and would i connect a wire there?..


Just to make sure

12v red to constant radio

switched 12v yellow ignition ground to the ignition wire of the radio

black ground to ground of the radio

[Selectron]

Originally Posted by chrisanthony

yes you are correct..that's exactly how i have it hooked up rite now...after i got home i saw the top led melted i assume that's due to directly being in the sun all day..what do u think?

Crikey, that doesn't sound too good! The LED is unlikely to melt - if it got that hot then the semiconductor junction within it would simply quit and it would no longer illuminate - is it the unit's plastic casing which has melted rather than the LED itself?

[Selectron]

Originally Posted by chrisanthony

I'm not exactly clear on this..what do u mean buy room and radio fuse..its through the fuse box? and would i connect a wire there?..


Just to make sure

12v red to constant radio

switched 12v yellow ignition ground to the ignition wire of the radio

black ground to ground of the radio

Yes, those connections are correct.

I only mentioned which fuses feed the radio for the sake of completeness. You don't have to go near the fuse box if you'd rather not - you can just splice into the wires at a convenient point behind the radio.

[chrisanthony]

Originally Posted by Selectron

Yes, those connections are correct.

I only mentioned which fuses feed the radio for the sake of completeness. You don't have to go near the fuse box if you'd rather not - you can just splice into the wires at a convenient point behind the radio.

hi...i just came back in from trying what you suggested. I connect all the wires..12v led to constant (radio), yellow ground to ignition switch (radio), black to ground and the LED still seems to be constant even through the key is turned to on..just to make sure..i am splicing into the radio harness...