You are one lucky people for sure. Dud he gave the reason why he was selling the kit?
If you like to download HFS-5 v10 user manual, you can use the following link:
Call Jeff at Howerton Engineering, he should be able to help you out, he should have Aquamist spares.
Jeff Howerton
Howerton Engineering
707.685.6279
Answer to your question: you need injector pulse signal signal for sure. The system can be set to trigger by boost or IDC%. Read the user manual, it is all in there.
Richard