Car Alarms

The alternator is maybe 3 phase, but it's rectified before it leaves the alternator.
Given that you say the car has a digitial dash, then it'll most likely have a dual output alternator, controlled by the ECU, however, one of those control wires will still essentially work like a conventional battery warning light wire.
The car may have an engine run relay for controlling some circuits.
What car is it?

Well I remember that on Vauxhall Astra's (circa 1987), the way the dim headlight circuit worked was by taking a line from the Oil pressure switch in order to make the lights go full brightness when the engine was running and the sidelights were switched on. That might give you something to go on.
Cheers,
Rob.

The fuel pump will only receive a supply when the engine is running or being cranked over, how about tapping into that? Probably won't work if it's a Diesel though. Martin

Well I'm assuming it's outputting three phase as it has a thick ground wire bolted on the outside and then three extra terminals all of equal size with wires connected that goes off behind the engine. I can't see what else would require 3 wires......
It's a Focus C-Max which apparently has a "Smart Battery Charging System" (your guess is as good as mine) so I've no idea how it compares to other cars.
I've been told by someone to use a voltage triggered relay set around 13.5V as when the alternator kicks in it bumps the voltage up to 14V but I'm sure that a fully charged battery can hit 13.5V.......
Cheers,

It's not a thick ground wire...
If you want to send me an email to moraycuthillgooglemail.com, with the reg (might be wise to include the chassis number if you've got it handy, in case the reg isn't on ford's system), and what engine it has, I'll have a dig around the wiring diagrams tomorrow night at work, and see if there's any easy way to get an engine run signal.
Not for a remote start system. Voltage controlled relays close just above 14V, but the vehicle battery needs to get that high first, which at idle can take a good few seconds after the starter has stopped.
Have you considered how you're going to get around the immobiliser? The vehicle won't start without a valid key/transponder within range of the ignition barrel (or the car if it's a keyless entry one)
moray

That would be a great help, thanks,
You mean a voltage triggered relay actaully exists off the shelf? I never realised and was going to make one....
The immobilser isn't a problem, there's a transponder bypass module that you put the top of the key in and it has a coil of wire that you then wrap around the ignition barrel. When it goes to start it, it makes it seem as if the key is in there. Not ideal leaving 1/2 the key in there but I guess you just have to secure it well enough.
I'lll get all the details and email you when I have them,
Cheers,
Michael