2019 Mercury 40 ELPT EFI (3-cyl) cranks, won't start. No key-on beep, no relay click, no fuel pump hum. Power and ground look good at ECM.

[northeast_bass_guy]

Engine: 2019 Mercury 40 ELPT FourStroke EFI, serial 1C567275. Console steer with remote control, power trim.

Symptoms:
- Cranks normally, never fires. Ran 3 weeks ago on a weeklong trip.
- It used to beep and make a click/clunk under the cowl when I turned the key on. Now there is no beep, no click, and I can't hear the fuel pump prime.
- Engine ran fine about a month ago. Freshly charged battery (13 V), and it was just serviced for the season (didn't start before or after servicing).

What I've checked:
- All engine fuses intact. Stop switch/lanyard in run position.
- Unplugged the round remote control plug at the engine. On the engine-side half, pin A (red) has constant 12 V, and pin C is the purple wire.
- Jumping A to C (fused jumper) puts 12 V on C, but nothing happens: no beep, click or pump hum.
- Cleaned and reseated the round plug. After that, with everything plugged in, the purple wire at the ECM connector reads 12 V with the key on and 0 V with the key off, under load. So the key circuit seems fine.
- At the ECM connector (harness half, ECM unplugged) I believe the constant feed, key-switched feed and grounds all read good. The black wires I tested read about 12 V with the red lead on battery positive.
- Reseated the ECM plug. No change.
- I can't find a separate relay under the cowl.

I ordered a SmartCraft Connect Mobile module to see if the ECM talks to the Mercury Marine app, and I may take it to a dealer for diagnostics.

Questions:
1. Has anyone seen this on a 3-cylinder 40 EFI, where the key circuit is good, power and grounds are good at the ECM, and it still won't wake?
2. Is there a main relay on this engine, and where? Or does the ECM handle that internally?
3. Where does the key-on beep come from on a console rig: the ECM, or the control box/key harness?
4. If it is the ECM, is there anything I should check before replacing it, like the fuel pump connection or draw, so I don't kill a new one?

Happy to post photos of the ECM connector and the cap if that helps. Thanks.

 

[AllDodge]

Is there 12V on the purple wire when the key is turned ON?
Have you jumper across the contacts of the stop switch to ensure switch has not gone bad?
Check for 12V on purple wire at the motor
There should be a main power relay but I'm not seeing one in the parts list

https://www.mercruiserparts.com/40-hp-efi-3-cyl-1c456300-up

 

[northeast_bass_guy]

12V on purple at the motor with key ON: Yes. I back-probed it and it’s getting to the ECM. I can cycle the key ON/OFF and I see the voltage change (12V to 0). Grounds seem OK at the plug as well.
Stop switch jumper: I haven’t tried this yet because I’m not sure where the stop switch is. Is it at the helm or on the engine? Where should I look for it?
Main power relay: I couldn’t find one either, and it isn’t in the parts list. All my fuses are good.

Thanks

 

[AllDodge]

The man overboard stop switch will be at the helm, and can be part of the throttle control or separate at the helm. There is a cord attached to it which gets attached to the driver. The cord can be removed and the switch turned on but that defeats the purpose of why it's there

Pic of just one type, can look different

https://www.walmart.com/ip/Mercury-...B3&conditionGroupCode=1&veh=seo_fpl&cn=google

 

[northeast_bass_guy]

Oh yeah I checked that. I have made sure the switch is in RUN when cranking and troubleshooting.

If I need to open that throttle assembly up and jump that switch that's going to be a problem because the screws that mount it to boat just spin like theres nuts on the back and the throttle is mounted to an aluminum box thats riveted to the actual boat... this is the exact throttle assembly I have:

Throttle Assembly

Thanks!