12V supply ignition switched feed in engine bay

[davetech]

Hi.
Could anybody please enlighten me as to where I can find a 12V supply which is ignition switched, in the engine bay of my 2.2 TDCi ?

[Dr Muse]

To take what load? There are a few but nothing you can use to power anything substantial

[davetech]

Only needs to provide half an amp (6W).

[davetech]

Can anybody help?

[Mirez]

I assume this is for something like DRL's?

You'll need to make your own ignition source in the engine bay, everything in there is either low current or signal sensitive so putting a load (which will probably create noise) on anything like that is a big no-no.

The best way is to bring a signal wire in from the cabin and then switch a relay direct from the battery which will give you a clean, isolated supply.

[davetech]

Thank you for the reply Mirez; was beginning to think I was alone out there 

[Mirez]

No worries, a lot of the Mk3 stuff is still new although they are getting into the DIY'ers mitts more and more now so the knowledge may increase. Electrical stuff is also a voodoo art to a lot so it can be a pain to get electrical info!

Anyway hopefully that's a good solution, the only final alternative is to grab the signal wire from a controller in the engine bay. I highly recommend NOT doing that though unless you are really stuck

[davetech]

So where might I find a signal wire in the engine bay?
I'm looking at either operating a relay or more likely a NPN transistor, as my required current is so low.
The isolation provided by the transistor would also eliminate any risk from noise.

[Mirez]

Theoretically you can grab it from anything that requires a constant power. Therefore any control module, the ecu itself or things like throttle bodies or even the MAF. If you are using the tranny then it's not so bad but I really wouldn't switch a relay with any of those supplies though.