Need input on 2012 R29 voltage drop at key on

[tugnnaweigh]

Chasing a voltage drop at the ignition switch. Have good 12/13 volts on input line until I turn the key on (first position, accessory) and then voltage drops to .4 volts on both input and output line.

If I disconnect the purple output line at the ignition switch 12/13 volts show at both poles so the switch itself seems good.

Yep, checked and redid all grounds and positive connections, checked all fuses and solenoids and breakers, added additional ground strap from engine battery to engine, checked and redid hot and ground leads to ECU, have 12 volts showing at ECU as long as the keys not on.

I figured amps had to be being pulled to drop the voltage that much so I put an amp meter inline to the purple wire and there no amps being drawn although the voltage did still drops on both input and output lines.

Yanmar tecs I talked to say the purple line goes directly to the ECU, bringing it to life and it distributes power from there bringing everything downstream to life and that makes sense to me. So I disconnected the ECU and the voltage at the ignition switch went from .4 volts to .9 and Yes, I realise the ECU likely isn't going to turn itself on until 10.5 or so volts but it was pulling that half a volt so the circuit to it is intact.

So it seems like the purple line is just soaking up voltage not carrying it and I’ve seen that before in boats, electrical lines that built up enough internal resistance they stopped carrying voltage.

So any experiences and suggestions are welcome, I'm thinking I need to know where the purple line terminates and what it terminates into in case the cure is to replace the purple line or whatever the heck it terminates into.

Aslo, doe’s anyone know where up the Yanmar food chain to send the ECU to get it checked? No luck on that with any shop nearby or Ranger Tug. Thanks in advance.

 

[knotflying]

Did you load test the batteries? How old are they?

 

[BB marine]

I'm not sure what power plant you have Volvo or Yanmar. I know on the Volvo and assume to be the same with Yanmar. When the ignition switch is activated the battery switched terminal only turns on relays. I will use my C26 Volvo as example. When I activate the ignition switch. The switched terminal (your purple output lead) activates a relay to turn the display panel on, activates the fuel pump relay, it also activates accessory relays. Volvo does not want the engine management system to be tied to any higher current draws so all it supplies power to relays and the relays when activated carry the current to electrical draw components. Relays do not operate for free! Relays don't draw much but the do have resistance and resistance causes voltage drop. Not much but some relays will cause a voltage drop of as much as .5 volts. If your problem of voltage drop has increased over time and you have a system as I described there is a possibility that the connections at the relay may have corrosion. Corrosion increases resistance and can cause additional voltage drop.

I'm not saying that this is your issue but just an idea. I know I have relays operated off my ignition circuit. I installed an additional relay this winter when to power my water flow and exhaust temp alarm. The power for this system is from the fuse panel. The power lead goes to a relay. The relay is activated by the ignition. The relay supplies the alarm system 12V from the fuse panel. As long as ignition is on the relay is activated.

I have never checked the voltage drop at the switch when activated so I can't give a value.