12v Accessory Wiring Problem

[sam.bresland]

Hi everyone,

I'm hoping someone can help me solve my problem. I've searched everywhere and cannot find what I'm looking for. (or I'm searching the wrong things).

I have an accessory that receives power when my ignition is on. What I would like to do is include a switch in this circuit, to break the circuit and cut the power to my accessory. But... When I turn my ignition off and then back on I want this circuit to be closed (my accessory has power). Basically the accessory is always on, unless I manually switch it off with a switch. I don't want to have to switch it back on, but instead it automatically switches back on when I turn the ignition off and on again.

Thanks in advance, I hope I have clearly explained it.

 

[Spoon]

Correct me if I'm wrong but it sounds like you need some sort of latch system, which is always latched On but you switch the latch Off with a momentary pushbutton. Similar to like a starter motor, but linking out the start button.

 

[Spoon]

I can't read the full description of this item, but you could ask the seller if this will do what you want.
Does your 'accessory' take more than 10A?

 

[sam.bresland]

Thanks for your reply. A momentary push button, would mean that I would push it and it would spring back on as soon as I release the button ?

 

[Spoon]

Thanks for your reply. A momentary push button, would mean that I would push it and it would spring back on as soon as I release the button ?

Yes, that is correct.

 

[sam.bresland]

I actually need it to be able to be switched off, for example I would drive somewhere with it switched off via the switch. Then turn the ignition off, and start the car again, without having to touch the switch this accessory would have power.

But maybe it's just not possible what I have in my head.

Thanks

 

[Spoon]

Similar to like a starter motor, but linking out the start button.

OK, I'm incorrect in this bit..

 

[Spoon]

I actually need it to be able to be switched off, for example I would drive somewhere with it switched off via the switch. Then turn the ignition off, and start the car again, without having to touch the switch this accessory would have power.

But maybe it's just not possible what I have in my head.

Thanks

Yes. Whenever you switch on the ignition the 'accessory' will be latched On. The only way you turn it off is by the Momentary Switch or turning off the ignition.
What is the 'accessory'?
What current does it take?

 

[shaun1]

I think you could a achieve this with a relay with both normally open And normally closed contacts. 12v from the ignition feed would go to the COMMON pin on the realy. The NC contact would feed the accessory. The NO feed would go to power the relay coil. The other side of the coild would then connect to ground.

You would also need 12v feed to go via your switch (which would need to be a non latching push button of some kind) to the relay coil.

When you push the button the relay will change over from the NC contact (disconnecting your accessory) to the NO contact (powering it's self). It will hold it's self in this position until the power is killed (ignition off) when in will switch back to the accessory ready for next time you start the car.

 

[sam.bresland]

I think you could a achieve this with a relay with both normally open And normally closed contacts. 12v from the ignition feed would go to the COMMON pin on the realy. The NC contact would feed the accessory. The NO feed would go to power the relay coil. The other side of the coild would then connect to ground.

You would also need 12v feed to go via your switch (which would need to be a non latching push button of some kind) to the relay coil.

When you push the button the relay will change over from the NC contact (disconnecting your accessory) to the NO contact (powering it's self). It will hold it's self in this position until the power is killed (ignition off) when in will switch back to the accessory ready for next time you start the car.

This sounds pretty much spot on, I appreciate your help. I'm going to have a try and get this to work. I'll let you guys know

 

[Devonchris]

This might be what you are looking for?

Cartek Fog Light Switch Control Unit | Demon Tweeks - https://www.demon-tweeks.co.uk/motorsport/accessories/cartek-fog-light-switch-control-unit

If your accessory is powered via a normally closed relay, then this switch can be used to turn it off. When you turn ignition off it will come back on again.

I've no experience of this unit but it looks like it will do what you want?

 

[Devonchris]

At a guess, you want to power a dash cam, which you want to turn off when it suits you. But don't want to forget to turn on again when you slow down?

Naughty.

 

[sam.bresland]

At a guess, you want to power a dash cam, which you want to turn off when it suits you. But don't want to forget to turn on again when you slow down?

Naughty.

Yes that's correct. Good guess!

 

[sam.bresland]

This might be what you are looking for?

Cartek Fog Light Switch Control Unit | Demon Tweeks - https://www.demon-tweeks.co.uk/motorsport/accessories/cartek-fog-light-switch-control-unit

If your accessory is powered via a normally closed relay, then this switch can be used to turn it off. When you turn ignition off it will come back on again.

I've no experience of this unit but it looks like it will do what you want?

Thanks for your help! This is pretty much exactly what I needed.

 

[Squid]

Run a cable from the battery and include a switch in the circuit, stick a post it up on the windscreen, "don't forget to switch the switch on or off Donk"