Merc 377 MAG DTS AXIUS electrical issue

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silver_power

Petty Officer 1st Class
Joined
Jul 8, 2009
Messages
327
Hello, i have a Cobalt 303 with twin 377mags dts Axius Gen1 and i want to make a question ...
With the battery switches OFF, when i turn the keys, i see at the instruments (Smartcraft) voltage reading 8-8,5V, at both engines. Obviously from clean power.
With the battery switches to ON, (starboard battery 1, port battery 2)the voltage reading goes to 12,5V.
Batteries are measured both 12,5V.
Why this happens? What should i check and which cable must i trace to check?
Thank you!
 
dingbat

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,313
silver_power said:
Hello, i have a Cobalt 303 with twin 377mags dts Axius Gen1 and i want to make a question ...
With the battery switches OFF, when i turn the keys, i see at the instruments (Smartcraft) voltage reading 8-8,5V, at both engines. Obviously from clean power.
With the battery switches to ON, (starboard battery 1, port battery 2)the voltage reading goes to 12,5V.
Batteries are measured both 12,5V.
Why this happens? What should i check and which cable must i trace to check?
Thank you!
Click to expand...
Sounds like you have a dead battery

Make sure the terminals need to clean and shiny. If that isn’t the problem the Batteries need to be load tested.
 
S

silver_power

Petty Officer 1st Class
Joined
Jul 8, 2009
Messages
327
If the batteries were dead, would the voltage reading go to 12,5v when the switches go to ON?....Batteries are measured OK......
Something else is happening and i can not find it...
 
alldodge

alldodge

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Staff member
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Messages
42,537
Bat switches off and the key is turned on. So all power is being feed through the keep alive power. There is voltage drop with that small wire

Edit: not counting all the circuits being back feed
 
C

Cdn20valve

Seaman Apprentice
Joined
Aug 10, 2015
Messages
47
silver_power said:
If the batteries were dead, would the voltage reading go to 12,5v when the switches go to ON?....Batteries are measured OK......
Something else is happening and i can not find it...
Click to expand...
Two things to check. first, your gauge might be bad. Check with a voltmeter.

Second, you may have a bad ground somewhere. what you can do is trace back all the grounds and see if something is loose. check the actual batteries first. make sure the ground connection is clean. Use the voltmeter to check all the power and ground leads.
 
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silver_power

Petty Officer 1st Class
Joined
Jul 8, 2009
Messages
327
Batteries have connection with 1. Clean power harness , 2.Accessories power harness, 3. Power Trim harness.
Everything seems OK, except that for some reason, the negative lead (ground) of Accessories power harness, is NOT connected to battery Negative.
This happens to both engines.
I do not have any power issues to the boat, except this strange issue with the low voltage reading at BOTH Engines with the batteries switches OFF.
 
dingbat

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,313
silver_power said:
Batteries have connection with 1. Clean power harness , 2.Accessories power harness, 3. Power Trim harness.
Everything seems OK, except that for some reason, the negative lead (ground) of Accessories power harness, is NOT connected to battery Negative.
This happens to both engines.
I do not have any power issues to the boat, except this strange issue with the low voltage reading at BOTH Engines with the batteries switches OFF.
Click to expand...
Why is the accessories ground disconnected?

A ground leak through a different circuit will cause the condition your describing
 
S

silver_power

Petty Officer 1st Class
Joined
Jul 8, 2009
Messages
327
As i bought the boat used, the negative lead was disconnected and covered with tape at both engines. So i supposed that it was done as it should.
So, i will check it with a meter and i will connect it to negative lead at battery.
To make something clear.....
1. The Power Harness is connected directly to battery with a 40amp fuse and to a 6-way terminal at the dash to give power? and it is also connected to junction box through the power relays?
2. The clean power harness is connected directly to battery with 5amp fuse and to the harness?
 
dingbat

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,313
silver_power said:
As i bought the boat used, the negative lead was disconnected and covered with tape at both engines. So i supposed that it was done as it should.
So, i will check it with a meter and i will connect it to negative lead at battery.
To make something clear.....
1. The Power Harness is connected directly to battery with a 40amp fuse and to a 6-way terminal at the dash to give power? and it is also connected to junction box through the power relays?
2. The clean power harness is connected directly to battery with 5amp fuse and to the harness?
Click to expand...
The only way to get 8.5 volts from a 12.5 source is by resistance or excess current draw.

Current flows from positive to ground. A bad connection/wire (increased resistance) can be on the supply or ground side of the circuit.

To troubleshoot this properly, you need to dig into the schematics to see where and how the voltage is read by Smartcraft.
 
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