How do I make a 12 volt, touch sensitive momentary switch to start a car?

I would like to create a touch sensitive panel that will allow me, through contact, to activate the starter on a car.

From what I have read on Instructables in the past, there are several ways to make 120v swtiches like this through the use of metal objects.  These have all been On-Off switches for things like lights or sound.  I would like to create a momentary switch that activates by touch in a 12v system.  If it is possible to do through a metallic contact point that already exists (part of the dash, or a trim bezel for example) that would be ideal.  All I really need is some kind of activation mechanism that transfers enough current to flip a relay when I touch it and that will stop when I remove my hand.

Anyone have any ideas?

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ae86boy (author) 7 years ago
I should have provided more information and asked the question more specifically...sorry guys.

Its going into an older car...so there are no computer chips or anything to worry about.  The car *is* EFI, but it is a 1989 model so there are no transponder keys or other electronic nannies to worry about.

Can I use the suggestions below to use *any* metal object as a switch, or are there restrictions to materials, locations, etc?  Can I trouble someone to draw me a simple MS Paint-type sketch of exactly what this would entail?

Ideally, I'd like to use the bezel off one of my aftermarket gauges (which is aluminium) to start the car through touch.  I have seen the link steveastrouk posted, but will it work in a 12v system?  I thought it was 120v specific?
Have u figured this out
ae86boy (author)  Sealab10285 years ago
No I have not. I haven't given up on an answer being out there...I just haven't found it yet and I've run out of ideas where to look.
orksecurity7 years ago
Note that these days, starting a car requires that the key be electronically recognized... so at most you're going to be able to replace that last little bit of key rotation which engages the starter relay. You will still need to insert the key and rotate it to unlock the wheel and the computer.
lemonie7 years ago
You would probably be best with a high-current (not voltage) relay for your mains-switching (as you mention). Operate that with a Darlington-pair. You bridge the +ve supply to the base of the transistor (left) with your slightly-conductive finger.

L
Try this: This guy has done exactly what I would suggest you do !

https://www.instructables.com/id/DIY-Touch-Sensor/

STeve