OMC 5.0L Wiring Diagram

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Tgibson94

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hello everyone, So Today i am taking my cracked mercruiser 5.0l out and replacing it with an OMC 5.0L, issue here is the existing 10-pin plug on my boat is a male connection. The OMC 5.0l 10-pin connector on the block is also a male connection.

so im looking at cutting the female end off my 5.0l mercruiser and splicing it on the correct connection type on the OMC Motor, im in need of the wiring diagram for the OMC in order to keep it the same. cant seem to find any on the web.
 

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Bondo

Bondo

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Tgibson94 said:
hello everyone, So Today i am taking my cracked mercruiser 5.0l out and replacing it with an OMC 5.0L, issue here is the existing 10-pin plug on my boat is a male connection. The OMC 5.0l 10-pin connector on the block is also a male connection.

so im looking at cutting the female end off my 5.0l mercruiser and splicing it on the correct connection type on the OMC Motor, im in need of the wiring diagram for the OMC in order to keep it the same. cant seem to find any on the web.
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Ayuh,.... Welcome Aboard,..... It'll be a hell of alot easier to just swap the Merc wirin' harness over to the new motor,....

Matter of fact, yer life will be much better, to strip All the OMC stuff off the motor, 'n redress the long block, with all the Merc dressin's,....

Otherwise, that cannon plug will be the least of yer problems,....
 
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Tgibson94

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Bondo said:
Ayuh,.... Welcome Aboard,..... It'll be a hell of alot easier to just swap the Merc wirin' harness over to the new motor,....

Matter of fact, yer life will be much better, to strip All the OMC stuff off the motor, 'n redress the long block, with all the Merc dressin's,....

Otherwise, that cannon plug will be the least of yer problems,....
Click to expand...
Problem is I'm missing the pcm from the Merc. Will it not work correctly by tracing everything down and wiring it the same as the merc was as far as sensors and such go?
 
Scott Danforth

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Take your 5 liter OMC and unbolt everything OMC bolted to the GM block and heads and throw away

Now take all the Mercruiser stuff on your busted GM block and bolt onto the other block
 
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Tgibson94

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Scott Danforth said:
Take your 5 liter OMC and unbolt everything OMC bolted to the GM block and heads and throw away

Now take all the Mercruiser stuff on your busted GM block and bolt onto the other block
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Just went to switch over the merc engine coupler and found out the flexplate is different. Took the merc flex plate and tried bolting it up, but the inner hole diameter is different.

This omc was a direct drive/tilt motor. Do they make an omc engine coupler so I can use the omc flexplate etc.

Also looking at the exhaust headers, the merc won't bolt directly up.
 
Scott Danforth

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Are you mixing 1985 and older 2-piece RMS motor parts with 1986 and newer 1-piece RMS parts?


Because it won't work

What years are the motors
 
Lou C

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That explains it then. The 1984 engine is a 2 piece main seal engine and the 1997 is a 1 piece main seal engine. The flywheels are different & that’s why the Merc coupler won’t fit the OMC flywheel. Not sure how to work around this….
 
Lou C

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When replacing engines you can’t mix years that are not part of the same basic series with the exception of changing a one piece main pre Vortec with a Vortec (all of which were one piece main seal engines).
This is a change GM made has nothing to to with OMC or Merc they just had to change their couplers to fit the changes GM made. You need a 1986 or newer engine….
 
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Tgibson94

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Missed it by 2 years. Damn. Thank you for all the help. New to boats and picked this project up.
 

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Bondo

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Tgibson94 said:
Just went to switch over the merc engine coupler and found out the flexplate is different. Took the merc flex plate and tried bolting it up, but the inner hole diameter is different.

This omc was a direct drive/tilt motor. Do they make an omc engine coupler so I can use the omc flexplate etc.

Also looking at the exhaust headers, the merc won't bolt directly up.
Click to expand...
Ayuh,.... If you want to continue down this course, you need a Chevy Flywheel for an 85, 'n earlier 305/ 350, in the same diameter as the one from the boat, probably 168 teeth,...
A Flywheel from a standard shift trans will also work, as the coupler uses the clutch pressure plate holes,....

Lots of 'em around, not really a big deal, except for one possible problem,.....
Is there 2, or 3 starter mountin' holes in the block,..??
If 3, No problem, if 2, yer right, that block is of no use to ya,....
 
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Scott Danforth

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I would get a 1996 or newer motor. And yes, the old OMC motor was a waste of time and money
 
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Tgibson94

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Bondo said:
Ayuh,.... If you want to continue down this course, you need a Chevy Flywheel for an 86, 'n later 305/ 350, in the same diameter as the one from the boat, probably 168 teeth,...
A Flywheel from a standard shift trans will also work, as the coupler uses the clutch pressure plate holes,....

Lots of 'em around, not really a big deal, except for one possible problem,.....
Is there 2, or 3 starter mountin' holes in the block,..??
If 3, No problem, if 2, yer right, that block is of no use to ya,....
Click to expand...
Even though the omc motor is an 84?
 
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Tgibson94

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I'm also looking at welding up the merc I have and seeing if it'll hold water. Only issue is when I bought the boat, the merc didn't have the ecm with it. Any help finding an ecm for it? The original 861925T3 ecm is no longer sold and I can't find the new replacement conversion kit for it anywhere.
 
Bondo

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Tgibson94 said:
Even though the omc motor is an 84?
Click to expand...
Oops,... My bad, got that backwards,..... I'll edit the above,.....

Btw,.... What are you callin' the ecm,..??
I thought this is a carbed motor,..??
 
Lou C

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If its got an ECM controlled efi system (probably throttle body EFI) and no ecm, there was a place that could repair these, maybe you can contact them & see if they have spares.
Otherwise, see what intake you have, you might be able to simply convert back to a simpler (and better IMO) carbed engine. You'd need a carb style intake, and a low pressure electric pump, unless using a pre-Vortec engine then its even better you get to use a cheap and reliable Carter mechanical pump.
I'd take the opportunity to go with a nice 4bb, Edelbrock is easier if you have a Merc. Carbed engines are not subject to Merc's making parts NLA. Because all is available from Edelbrock & Holley, pumps from Carter. I can even get just about any part I need for a Quadrajet that hasn't been made in over 30 years.
 
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