My sister-in-laws Citroen ZX (H reg) won't start.

The fuel is getting through okay. Basically it has no spark, so won't start.
I've tested all the fuses, which are fine. The coil has 4 wires going to it,
they're from the distributor I think.

Can you give any indication of what the connections are?

Where can I find a wiring diagram for the ignition on the net. please?

BTW Its not a traditional coil with two terminals, but a square block with a
connector containing 4 contacts. If I knew what each contact was for I would
check it, hence asking for a wiring diagram.

What are the common failure points with this car/model to cause this
problem?

It was running okay one moment, then on the way to the mot station it
stopped, I thought it was lack of petrol, so put a couple of gallons in.
Ended up flattening the battery trying to start it, so towed it. It did fire
up for about 20 seconds, but by the time I got out of the car to remove the
tow rope it had stopped. Towed it for about 2 miles, but it never fired up
again.

Any help is appreciated.

Thanks for looking.