GT 40 cutting out at high revs

Welcome from Australia great site. Have a GT40 in a 97 Nautique with 300 hrs have had an issue with the motor cutting out intermittently generally at high revs 4500. It's then possible to start it again as the fault clears. Initially thought it was water in the fuel,cleaned the tank and changed the filters. Changed the plugs still no luck. Checked fuel pressure 45psi all good. Back in the water yesterday failed again no spark out of the coil. But the fault cleared before we could find it. Restarted took revs up to 4000 and my auto elec gently tapped the three relays on the back of the motor. Shut down straight away. Replaced the relay that powers the ECU problem fixed. Hope this helps someone. Cheers Gus