cranking voltage check 12 v - 5 v fluctuate

tavacska

Petty Officer 1st Class
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Jan 21, 2017
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Today, I was ready for the lake test of my rebuilt 1977 mercury 1150.

It was running good a week ago on flush. This week, I cleaned the boat and rewiring the dashboard, routing the cables and wires, and installed the electronics.
Before I leaving for lake, I tried to test the motor. It won't crank.

1. I checked the battery, 12.4 volt.
2. the voltage in the switchboard red and white is 3-9 v.
3. check the voltage on battery terminal, 12 volt.
4. Then I rotate the cable terminal at battery. The voltage in the switchboard become 12.3 volt.
5. Then I tried to crank, no work. I tested the voltage in the switchboard, it becomes again 3-9 volt. I mean 3-9, it differs each time of the test cycle, but mostly around 5-6 volt.
6. But the terminal at battery is always, 12.4 volt.

Something is wrong, what could it be?

I tested all the control cable continuity and all good. I do check the wiring and try to simplify it by removing no important stuff, like tachometer, neutral switch.
It is still the same problem.

When I tried the Fish finder, it works.

Please help.
 

ondarvr

Supreme Mariner
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Apr 6, 2005
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11,527
You have a loose and or corroded wire or connection, check everything again, rotating a cable shouldn't change anything unless there's a problem.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Clean all the connections so you see bright shiny metal. Clean enought to eat off of.

If any battery cable looks suspect, replace it. If any cable is green from corrosion, replace it

When your done and everything is running perfectly..... Seal all the connections with marine electrical varnish
 

Chris1956

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Mar 25, 2004
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look under the insulation on the battery cables for a bulge. A bulge implies corrosion. Second step is to check the quick disconnect. I never had an issue with the battery cables there, but I had the white wire break there, which was a drag. Using a jumper cable from the battery to the motor will help isolate the problem battery cable.
 

merc850

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What type of battery are you using, you can't use a maintenance free or AGM type you have to use a marine battery with non sealed cells.
 

gm280

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A lot of people assume that if they can read 12 volts at the battery and even at the dashboard and/or starter solenoid before trying to do anything, that the wires are good. However, voltage with out any serious current draw is not the same as voltage with high current flow. Remember the voltage is the pressure, sort of speak, while the current is the flow through the wires. So the wire can be too small in size, or have some corrosion anywhere in the run, even inside the insulation. So if you are having problems, clean all the terminals to bright shiny metal and if the problem still persist, then time to replace the wires. But not just any wire, It needs to be marine grade wires. There IS a difference. Regular stranded copper wire will work, but its life expectancy will be very short because of the conditions boats are subjected to. So buy the proper wire and gauge size for your circuits and happy boating. JMHO
 

roscoe

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What type of battery are you using, you can't use a maintenance free or AGM type you have to use a marine battery with non sealed cells.

Well thats news to me.
Someone should tell the battery manufacturers to stop making maintenance free marine batteries.
 

merc850

Commander
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They're OK if your motor has a voltage regulator but older Mercury outboards didn't need one.
 

tavacska

Petty Officer 1st Class
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Jan 21, 2017
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244
Thanks for all the replies.
I will do from the beginning.

I spent a lot time rewiring, routing the wires. But I must admit I am not confident that everywhere is and clean and solid. Because last week the tachometer doesn't work because of the dirty of connection of rectifier.

I will do this thoroughly again, though I am very hesitate to do so because of the time consuming.

But fortunately, it is Not the switch's problem.

BTW, I bought a marine battery Interstate from COSTCO, CCA 600, RC 160. Is this battery ok?
 

Chris1956

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Mar 25, 2004
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To be fail, Merc850 is correct on using a non-sealed battery, due to the fact that you cannot add water to them. However, the charging rate of the motor in question is pretty low, maybe 4A at cruise speed, with a good battery. It is likely the battery will wear out (about 5 years in my experience), before it needs water.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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I will do this thoroughly again, though I am very hesitate to do so because of the time consuming.

It is time consuming, however would you rather fix it right and fix it while on land, or not do it right and try to troubleshoot a problem on the water due to a no start situation when your miles from shore
 

tavacska

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Jan 21, 2017
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One more question.

I don't have the Engine wiring harness connector at the motor.
And I don't have the remote cable connector either.

I don't want to spend over $200 for the connectors from ebay.

What's the best way to connect the remote control cable and the engine harness?
(And I am now using the water proof connector.https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1)

And I am using 16 gauge wire for all the wiring. (motor and boat)
 

Chris1956

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OK, I will assume you want to start the motor to test it. On a '77 Merc 115HP motor you have battery powered ignition. To bypass the wiring harness do the following:

Connect battery cables (jumper cables are lousy, but acceptable) from battery + post to large red wire on starter solenoid.

Connect - battery post to large black wire on case ground behind fuel pump.

Connect jumper wire from red wire on starter solenoid to red and adjacent white terminal on switchbox.

Connect jumper wire from red wire on rectifer to red post on switchbox.

Make sure black wire on switchbox and rectifier is grounded.

Pull up on black manual choke knob on top cowling support.

Pump fuel line primer.

Connect flusher device

Jumper starter solenoid from large red wire to small yellow wire, to crank motor. Push throttle arm back a bit to advance throttle.

She should fire and could start.

You could make up a hard-wire harness from an ign switch to the motor. I can give you the connection table.
 

tavacska

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Jan 21, 2017
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244
Chris,
I did exactly as you said, and found out it can not crank either.
Then, I remembered I connected the power tilt engine cable to the battery cable too. They are connected to the battery cable and then together connected to battery.
When I disconnected the power tilt cable from the power tilt engine, it worked. Then I reconnected it to the engine to confirm it's the problem of the connection of power tilt. It still works.
And now it works and can crank with no problem. But I believe the connection and cable is the weak point. The battery cable is looking very good.

Whatever result I have, I will replace the engine harness totally with 14 gauge wires. And I will weld all the connectors.

Thanks all for relpies.
 

tavacska

Petty Officer 1st Class
Joined
Jan 21, 2017
Messages
244
Hey, guys,

I do the rewiring work from the engine to the control dashboard.
Every connector ring or spade connector, or screw is sanded shining.
Every cable and wire is new or very solid condition. I replaced the battery too.

You know what, it works.
The electric control wiring system is confirmed to be in solid working condition.
Thanks for help.
 
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