using 4v to switch12v ign live

Yep thats spot on-well thats how read it-so just need to recap on what connects to where please. Got the +ve from the led to the 100Ohm resistor the other side of that to the base of the transistor,the collector to 12v,the emmiter to the coil of the relay and the other side of the coil to ground-only thing i cant see is what the switch part of the relay has connected to it and where the 12v connection back to the device im switching goes-prob just me being thick-pmsl.thanks.

 hi Mri dont know if your out there or had a chance to read my last post-just a bit stuck at the mo.look forward to hearing from you.

You could have done this job in 5 minutes for less cost if you'd have listened to my post.

yep youre right Howie i could-but then i wouldnt have learned something new and if this doesnt come off then I will use your way but im in no real rush to do it either way-just enjoying the learning experience which is what lifes all about.

Your not wrong if it helps you to learn things, it's just that I have to do a job, efficiently and relatively quickly and most of all one that works first time.

You're (Howard) is just happy he didn't do the teaching... FYI - I tend to avoid the "low volt" actuation issues. I seem to have troubles conveying either get behind the LED or whatever (ie, to the actual "switch") else use a FET or (more likely) a transistor.   

apreciate you have a job to do and the way you have to do it Howie and thank you very much for the time you took to reply and explain,im the same in my job has to be right first time and in the quickest poss way which when youre building race engines doesnt always work-lol.know past the basics with vehicle electrics just want to get toknow more about the electronics side-always eager to learn.As for old spark-thanks for the post-Howies done his teaching in his own way-know what you mean about the low volt switching,I am using a transistor-well iwill be if I can get a little more info,then hopefully it will all work nicely if not Ill fry something (prob me!) and end up using Howies way-pmsl.