Mercruiser 140hp wont stop running

rgodales

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Apr 16, 2014
Messages
23
Good morning guys,

I really need some help here. So I installed a fuel gauge and a fishfinder on the dash of my boat. I had to remove the trim and tilt gauge and voltage gauge from the dash. Now the problem is that when i switch the key off it will not stop my engine. I notice that a wire, purple with a white tripe, is coming from the engine wiring harness. When i put the key on the off the engine rpm goes down a little bit like it want to stall but it will not die unless i let it run for a while. If i make + contact with the purple wire the rpm goes back to normal.

Any ideas what did i disconnected that I shouldn't have?

Is a 1970 starcraft capri with a 140hp merc. Thanks all for your input.

Thanks
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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47,306
if this just started when you added the fuel gauge and depth finder, my guess is you somehow tied the ignition back to power and are back-feeding the ignition. start by undoing your latest wiring changes.
 

seachest

Seaman Apprentice
Joined
Aug 20, 2011
Messages
43
I just went through this with my OMC Sea Drive - In my case I found that the magneto ground wire pin in the harness got pushed back and was not connecting. I thank Uncle Willie for his guidance check my posts (seachest) and his responses - I was going crazy too !
 

Lincoln253

Cadet
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Sep 26, 2014
Messages
19
You could have inadvertently tied the 12v lighting positive to the ignition post on the fuel gauge and if you did the ignition could be getting power through the lighting circuit Causing the key switch to stay hot After U shut it off.... Scott is right U are back feeding 12v from somewhere back into the ignition circuit
 
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rgodales

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Apr 16, 2014
Messages
23
I tried looking for the issue. Disconnected all of what i have done. Still same. Took it to a shop and they worked on it for 3 hrs and still can't find it. Everything works fine except that it will not shutoff. The shop said that issue is they adopted a new ignition to the old motor and they have no idea how they did it.

The strange part is that if i unplugged the entire harness under the dash it kills the engine asap. Not sure if this some sort of indication. I'm about to just unplugged all the gauges and see if that takes care of the issue.



Any other tips are welcome.
 
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Bondo

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Apr 17, 2002
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I tried looking for the issue. Disconnected all of what i have done. Still same. Took it to a shop and they worked on it for 3 hrs and still can't find it. Everything works fine except that it will not shutoff. The shop said that issue is they adopted a new ignition to the old motor and they have no idea how they did it.

The strange part is that if i unplugged the entire harness under the dash it kills the engine asap. Not sure if this some sort of indication. I'm about to just unplugged all the gauges and see if that takes care of the issue.



Any other tips are welcome.

Ayuh,..... With the plug yer unpluggin' at the dash, unplugged, will the motor start, run, 'n shut-down with the key,..??

Test by connectin' only 1 circuit at a time back on-line, at the plug to find the Issue,...
 

rgodales

Cadet
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Apr 16, 2014
Messages
23
Bondo,

Not sure what you meant with "With the plug yer unpluggin' at the dash, unplugged". Sorry very knew here.

By "Test by connectin' only 1 circuit at a time back on-line, at the plug to find the Issue" Did you mean to said i need to unplugged all gauges and wire them back up one at the time?
 
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Bondo

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Apr 17, 2002
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70,468
Bondo,

Not sure what you meant with "With the plug yer unpluggin' at the dash, unplugged". Sorry very knew here.

By "Test by connectin' only 1 circuit at a time back on-line, at the plug to find the Issue" Did you mean to said i need to unplugged all gauges and wire them back up one at the time?

Ayuh,.... You said, "The strange part is that if i unplugged the entire harness under the dash it kills the engine asap. "

So what did ya Unplug,..??
 

rgodales

Cadet
Joined
Apr 16, 2014
Messages
23
Ok i took the battery gauge and trim gauge. I have no need for them. Issue started first time out. I can turn it off if i unplugged the entire hardness at the dashboard. So something is back feeding at the dashboard? Or is just dying bec i'm killing power to ignition?

So confusing.
 

UncleWillie

Captain
Joined
Oct 18, 2011
Messages
3,995
When you disconnected the wire to the gages, what did you do with them?
Tape them up? Cut them Off? Tape them all together?

Is the Purple/White wire under the dash, or back by the engine? Is it connected to anything?

So is something back feeding at the dashboard? Or is just dying because I'm killing power to ignition?
Not an OR question! the answers are YES and YES!

And just so there are no misunderstandings, please confirm ...
This is not an Outboard Motor with a Magneto ignition?
It is an I/O Drive, with a 140hp Automotive type engine, with a coil and points style ignition? Correct?
 
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rgodales

Cadet
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Apr 16, 2014
Messages
23
When i disconnected the wires to the gauges i just had them sit there not touching anything.

The purple wire is coming from the trim sender-I think.

It's a mercruiser 140hp with alpha one stern drive.
 

rgodales

Cadet
Joined
Apr 16, 2014
Messages
23
I found the wire. It was a orange red thick wire. Not sure what is for but i just unplugged it from the ignition terminal at the temp gauge and connected the wire to the battery terminal at the ignition switch. My question now is, will this damage anything? It was connected to the battery before since it was connected to the + side of the temp gauge. So i'm assuming it should be fine now correct?
 
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