Ignition kill switch

[George 206cc]

Hi all (mine is an '04 1.6 petrol)

I'd like to install an ignition kill switch. I'm not too worried about theft, but I like to tinker and find these challenges fun.

Looked under the steering wheel at the ignition wires, poked a few with the multimeter with different key positions. There's a thick orange wire that goes together with a thick green earth-looking wire into a plug that plugs into the fuse box under the steering wheel. Both have 0V with no key, 12V with key turned. With that unplugged, the starter goes but the car doesn't spring into life. So, that's the wire to cut and put the switch on, right? Or is there a different wire I should use so not even the starter goes?

If so, what's the maximum current that will pass through that wire? I mean, what wire and switch current rating do I need?

Finally, any other general advice about this kind of thing?

Thank you!

George

[IanL]

To kill all three supplies switched by the ignition (including the starter), interrupt wire No. BF07 which goes from Pin 7 of plug 8V NR (black plug with 8 pins) on the engine compartment fusebox to pin 1 on the ignition key.

It's no good talking about wire colours, because Peugeot do not document the colours, and they vary between cars/factories/time of the month, etc. You have to use the wire No., which should be marked on it.

To determine the current rating, the supply is from MF7 (master fuse beneath the fusebox) which is listed as 30Amp.

EDIT: I would interrupt the wire with a relay - that way you can use lighter wire to your hidden switch.

[George 206cc]

Thanks for your reply Ian.

Found a relay that would do it, rated at 40A. Found a switch, wires, etc. As for connectors, I'm not sure what to do regarding connecting the (up to 30A) BF07 wire to the relay.

The relay has blade terminals of width 6.3mm. Would the yellow crimp connectors be suitable for handling the current, up to 30A? I've been looking online and getting mixed answers. Halfords reckon their respective crimp connectors for that size are good for 25A. What do you think?

Should the BF07 be soldered to the relay terminals instead? I doubt my soldering is any better...

EDIT: Does the passenger airbag switch do anything other than just close the circuit of the 2 wires that feed into it? I found with the multimeter that in the ON position, the circuit is closed. So if I was to get the wires and just connect them directly instead, would that be doing the exact same job? Or perhaps the switch has some resistance which is necessary in the circuit? If I can just connect the wires directly and it be exactly the same, then I may use that as the ignition switch. It's visible, yes, but what thief would think to disable the passenger airbag to help start the car?!

[IanL]

I would crimp with the correct tool and then solder. Belt and braces.

On balance, I would advise against using the airbag switch - if the car passes to someone else without reversion of the mod it could be bad news. Neat idea, though.

Are you familiar with the concept of a hold-on (or latching) relay? The first circuit here would do the trick. Use a momentary press button for the set switch. You press the button to close the relay contacts, and it stays on until the hold-on circuit is interrupted. If you wire the hold-on circuit from the ignition key switch (so the ignition key is the reset switch in the circuit), it will require the key to be on while the button is pressed to on to keep the relay closed, and once the key is turned off, it will not work again unless the button is re-pressed. That obviates the need for you to remember to switch the relay off when you leave the car.

You would not need the double pole double throw (DPDT) relay, because the cut ends of BF07 would be connected to 2C and 2NO (so 1C has no function). Just connect any ignition-fed point to K1, and K2 is connected to earth.

I doubt anyone is going to guess that one

[Capncol]

Not trying to be funny, but if you are asking such basic questions, should you be trying to modify the wiring?

The BSI is a delicate thing at the best of times. Corrupt that, and you are in a world of hurt.
Not sure what you wish to achieve as the standard system is quite secure in that it needs the code from the transponder in the key, and the codes from Engine ECU and BSI to match before it will start.

[IanL]

As the scheme does no more than interrupt the supply to the ignition key and the starter (which is what the ignition key does anyway) it cannot adversely affect the BSI. The supplies to the BSI which are not switched by the ignition are untouched.

The scheme is designed to frustrate someone who has somehow (burglary?) acquired the car's key.

[George 206cc]

Col,

I admit I'm not an expert on how these things work, however, what should be clear is my desire to learn. My "basic questions" are to enable that. With Ian's comments here, I'm learning more about this wiring. In the time you took to attempt to deter me from my ambition, you could have contributed to the knowledge in this thread to help me and many other readers.

And as Ian said, it's anti-theft for if someone steals the key via house burglary.

[Spitfire6]

Hi IanL,
I like the, as simple as circuits.
I use RS SR flip-flops all the time as a programmer. Nice to see its pure form as a mechanical thing!

Somebody steals your keys; They are still F***ed.

A little bit more ingenuity and you could have the horn latched if start attempted prior to resetting. Another SW to reset the horn. LOL.

Cheers,
Iain.

[IanL]

….A little bit more ingenuity and you could have the horn latched if start attempted prior to resetting. Another SW to reset the horn. LOL.

Diabolical

[George 206cc]

I watched a YouTube video that detailed how to involve the horn too. I decided not to go for that though because I'll probably forget a few times and I can't imagine the neighbours would enjoy that... Haha

[Spitfire6]

Hi,
Even though crimps are used by 100% of aircraft; I would not use them to connect to a relay. Buy a relay with a socket.
High IP even better. You will still need to crimp, but the relay contact area & reliability will be better.