need help with wiring layout for controlling additional rela

[Flaming_Crossbow]

Hi Guys,

I am working on a patch harness for a Magneti Marelli IAW 16 ECU to MS2 conversion for a MV Agusta (Ducati / Fiat / Lancia) system.

The sensors and accessories are pretty straight forward but can't figure out the ECU power and relays control... Unlike the conventional relay layout like the core wiring diagram in the MS manual with an ignition switch controlled Main relay + an ECU controlled Fuel relay,
MV Agusta uses the following:
- a main relay controlled by the safety switch (kill switch) / ignition key with a low power line to ECU. (middle relay in the diagram)
- a fuel relay (power relay) controlled by the ECU for the fuel pump,coils and injectors (equivalent to MS2) (bottom relay in the diagram)
- a main ecu power relay (Latch relay) for a high power line to the ECU also controlled by the ECU (top relay in the diagram)



The MV Agusta relay board is a single PCB I wish to keep stock.

I considered:
- GND Switching the Latch relay (OEM pin 4) with an unused MS I/O (not sure if possible).
-Bridging the Latch relay control wire with the Fuel relay control wire and doing something with the high power wires (not sure how).
-Keep the Latch relay unused but I doubt that the ignition switch controlled power line is up to the MS power demand and am unsure about unforeseen effects on the system.

Suggestions are very welcome.

[Matt Cramer]

If the latch relay wires go only to the ECU, I'd simply omit the latch relay and power the ECU off the main relay.

[Flaming_Crossbow]

Matt, i considered that but there is no main relay wire direcly going to the ecu connector. Only the wire via the safety switch. I don't know the power rating for the safety switch, i doubt that it is enough to power the ms2 ecu.

Right now i am trying to figure out how to switch the latch relay with the ignition and power the ms2 ecu via the (to be operated by the ignition key) latch relay. But the latch relay is part of the relay PCB so i can't simply rewire it. If the latch relay can be operated via some kind of layout via the ecu connector it would be great. Maybe the latch relay can be GND switched via another relay + an ignition switch wire?

[slow_hemi6]

Ms will run happily on a 2 or 3A fuse. Apart from IAC The MS is all ground switching. Some factory ecu's have high side (12v) drivers so they have larger 12v supply wiring but MS does not.

[Flaming_Crossbow]

Ms will run happily on a 2 or 3A fuse. Apart from IAC The MS is all ground switching. Some factory ecu's have high side (12v) drivers so they have larger 12v supply wiring but MS does not.

Thanks Hemi.

[LAV1000]

I am running a IAW 16M.A4 on a ducati ST2 engine.
Are you sure about the latching ?

On my bike it uses a relay to switch the sense wire from regulator to battery.
And I believe it also uses this wire to measure the battery voltage, to make right calculations for dwell time and injector dead time.
And to make sure there is enough voltage to start the bike.

Relay coil is switched to the low side and connected to 4.
Battery voltage/sense wire is connected to 35.
Main power is connected to 26.

And relay is time delayed (2 sec.) after switching main power off.