Does anybody know of a wire in the ST that is ONLY HOT (has power) when the engine is running?

I don't mean just when the key is turned to position 2 (ie ignition), I mean full on engine running.

Any help would be appreciated! Thanks.

theres always a permenant power in a car from the battery but nt sure if there is one when running. other than from the spark plugs??

The problem with the spark plug leads is that they pulse rather than being live constant. They're not 12v or useable either.

I'm struggling to think of anything that doesn't work unless the engine is running. Does the heated front windscreen still work without the engine?

what are you tryin to switch??

That's a tricky one! What about the steering pump?

Dare we ask why? Lol

I'm wiring in one of the Ford Power starter buttons and I quite like the idea of making it so once the engine is running the button becomes inactive. I think you do this by wiring a relay in hence stopping the button from outputting anything once the engine is running.

Unless anybody else has any bright ideas please?

Hehe.

you could use a timing circuit on a PCB too disengauge a relay after 30 seconds or so... i.e. after 30 seconds pushing the button will not start the car or engauge said motor, tell the timing circuit engises the Relay again for another 30 seconds...

a 555 timing circuit is what im thinking... very simple.. cheap too do and pretty easy... but for the life of me cant remember what sort circuit it needs too be bistable or monostable grrr

Put a little bit of plastic over the switch like what they have on the films when they launch a nuke lol

if that's the case of the front windscreen, there should be a relay. the relay delivers power to the front windscreen only when the engine is running. If you get to that relay (wherever it is?!) then you got yourself the wire you are looking for.

Yeah, front windscreen (when both sides are on) uses something silly like 60A of current, so would kill a battery in minutes.

You could tap in to the signal +ve from the alternator multiplug, but to be honest there's no need for it, as once the car is running the starter motor relay is inactive (relay/switch side goes from -ve to +ve) therefore no risk of 're-engaging' the starter via a start button. I've wired in a few of these and had similar concerns to you, until I figured out how it all worked with a multimeter etc.