Merc monitor low voltage reading (9.7) during cranking and missing horn all of a sudden when turning key

[twsykes]

Hey guys, I am struggling with a low voltage reading on the mercury monitor. For all I know this could have been this way for a long time but what triggered this was the solix graph throwing a low voltage on the graph during startup. I then began looking at the full screens on the mercury monitor and noticed it dropping what seems to be wayyy lower on the monitor vs on the graph. I also checked the voltage at the fuse panel on the the power and ground and the voltage did not seem to drop anywhere near the amount that shows on mercury monitor....

Am I right in thinking the mercury monitor gets its readings from the engine module directly via the mercury monitor connection?

Several other things I noticed.... One, the horn that usually turns on with the key no longer turns on and to me the ignition switch seems a little odd at times.... I had noticed it before today tho....

Any help? Attached is a video of what I am talking about. I am actually running 2 cranking batteries now and still getting this occasionally.... Thoughts? I tried to add a video but could not on this site.

 

[SLOmofo]

Myself....I think you are over thinking it.
On the stuff I worked on, during Cranking almost everything not necessary for start up should NOT be powered.
Whenever I went to start an engine, my automatic thought check list came into play.

1. Turn key to ON position, is everything happy. ie Dash lights bright. Dim, check the battery voltage then clean and tighten the battery connections.
2. Turn key to START/cranking. Does the engine turn over? Does it crank over normal speed?. Is the tempo even(compression check)?

3.Does the engine start and run?

12.6 was my minimum battery voltage.
9.5 was my rule of thumb minimum starter cranking voltage.

Customer drops off car for a major service when I'm not open. I jumped into the car and cranked it, started immediately, to quickly for my mental check list. Shut it off and cranked again, good everything normal....except...... after about 5 seconds run time a very loud BANG, loud hammering, very rough running and I see a raised bump in the hood. Shut it off, as I opened the hood another noise(something rolling). Hummm spark plug wire shouldn't be flung over there on the inner fender well and that hole in the hood liner.... O lookie here the spark plug.

 

[twsykes]

Haha. I may be overthinking it.... Thanks for the info

 

[twsykes]

Turns out the issue was my humminbird graph. I just had to send it back to them. They had seen the issue before. This is on my 2 seater boat.