The CA18 will not have a single coil, so the diagram may not be of much help for this fella. It's certainly possible to get the tacho to work. I did with the stock CA18 ECU.

I used the common 12V wire that feeds all coils after the transistor pack. This line was cut and I ran wires under the dash to connect to the 2 tacho inductive loop spade terminals.

The downside is that if this connection is broken, you lose power to the coils, and the engine will obviously stop working.

Cheers,
Chris.

ps. I vaguely remember the wire colour was solid red, but I'd need to check on the weekend. It's basically a common wire to all 4 coils (so all pulses run through the tacho loop), and I had used cheap spade connectors.. that's why I know the engine stops working when the link is broken.