Mariner 115 “Tower of Power” not starting

Chopp

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Aug 5, 2019
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I have a 1983 Mariner 115 I picked up not too long ago as a trade for an old 14ft aluminum boat, as a hope to put this on a pontoon. The needle and seat were bad on the lower carb, so I replaced that and that fixed my fuel problem. When I tried to start it, it cranked twice and it stopped. It’s a new marine battery, and it was cranking the motor the day before when I tried starting it up for the first time before I found the fuel problem. But when I connect the trim pump (engine is on stand) that doesn’t work either. It seems as the electronics aren’t working. I also tried tapping the starter, that didn’t work.
 

GA_Boater

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So nothing works? Clean all the positive and negative connections, one or more is not making good contact. When you're done cleaning all of them should be clean enough to eat dinner from.
 

jimmbo

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Is the Battery fully Charged? Batteries are known to fail internally, even new ones. Are all the connections clean and tight? Are the Power Cables in good Condition and not all corroded/eaten away inside or at the connectors?
 

Chopp

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No, nothing works. I mean I can’t really test anything other than the starter and trim pump, and I’ll try cleaning the terminals but it seems strange that it worked fine one day, then the next it dies after a crank or two
 

Chopp

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And I’ll check the wires themselves, I did pull the motor off of an old rotted out fiberglass boat
 

jimmbo

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When you were removing and reinstalling the carb(s), did you interfere with any of the Wires, or connections?
 

Chopp

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I took off a screw that must be a ground for a few wires that feed to some fuel component. Not sure what it is but a fuel line goes to it. And I removed a little box that was mounted in front of the card. But that’s it
 

Chris1956

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Run your fingers along the battery cables and feel for a bulge. Bulges under the insulation indicate corrosion.

Also, a motor that old may have engine wiring harness issues. Be sure to inspect it.

Finally, the battery ground is attached to the lower cowling. There are ground wires connecting it to the block (under the lowest cowling with the 115HP on it). The starter has it's own dedicated ground cable. Make sure it is in good shape.

Also, the PTT system usually has dedicated ground and power wires to the battery. They need to be clean.
 

Chopp

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The terminals were corroded, I replaced them with copper ones, still a no go. Wires themselves look solid. But nothing seems out of place... do you guys have any other ideas?
 

Chopp

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I remember, when I was going in for the carbs, there’s a little black box mounted to the metal panel that’s in the way of the carbs (sorry, I don’t know what a lot of stuff is called. New to boats) and when I took it off, it was wet. Not sure if it was water or something, but there was a significant amount of that liquid. Granted it worked that day before, but maybe that’s something? I believe I read on another forum that it’s some ignition or idle control module and someone said to take it off and tape the wires because it “destroys the engine.” I’ll try to upload a picture, but I need to figure out how to reduce the size of it. But also in the picture you’ll see a little yellow wire that’s hanging out. I believe it wasn’t connect to anything to begin with, but I don’t know where it goes and I don’t know if it’s important or not.
 

jimmbo

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Time to bring out a Volt Meter, and start checking Voltages, Voltage Drop, and Continuity.

Have you tried bypassing everything and using a pair of Jumper Cable go directly from the Battery, to the Starter and Ground?

That "little box" is most likely the 'Idle Stabilizer'. it was to electronically advance/retard the timing under some conditions at idle. It was never explained well in the Mercury Service Manuals, so it must have been something that was Worshiped as a Sacred Entity. A lot of People feel it should be treated like an 'Auto Blend' mixer, something to be removed and a competition held to see how far it can be hurled from the boat in deep water
 
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Chopp

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I’ll have to buy a volt meter. But by using jumper cables, you’re talking about going from the positive battery terminal to the ground of the starter? Just to see if it works? I did find a wire that broke within the harness, but judging off it’s insulation coloring I believe it’s for the trim pump. I’ll fix it, just haven’t got around to it
 

Chopp

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And also, when I’m testing the wires what am I testing for and where at? Both the positive and negative wires are black, and most of them are black and some yellow ones. But what’s the yellow wire on the starter for? It appears to go down towards where the fuel line connects to. There’s also multiple different wires connected to it. It was grimmy, so I sprayed it with parts cleaner.
 

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racerone

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The yellow wire is positive to the starter from the solenoid.-----Do not put positive to ground as you will get an impressive spark show !!
 

Chopp

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Okay. I hooked an extra wire I had, tapped it on the yellow wire and the starter popped to life with some sparks on the battery.. probably from a horrible connection since it was just a stripped wire. But nothing works by itself... so now I’m wondering if it’s that solenoid? I’ll get an electrical tester. Does anyone have a diagram that shows what the solenoid branches off to?
 

Chopp

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I used that wire, and I used the positive end and tapped other wires on that solenoid. Everything had a spark. Everything but to where the positive from the battery goes to the solenoid. I did this to test to see if I just have a bad positive cable. But directly on the solenoid, it doesn’t work. Would this mean the solenoid is shot?
 

Chris1956

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You can view a wiring diagram for your motor at the max rules web site. Solenoids are usually not a problem
 

Chopp

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I checked that diagram, saw there was a fuse. So I decided to check that first. Lone behold, it’s blown.
 

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Chopp

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Changed the fuse, and it worked.. for a second. Then that fuse blew. Why would that be?
 
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