1979 Mercury 140 wiring diagram

James_Ketcham

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recently acquired a 79 140hp outboard to put on my boat and almost every wire on the engine has the insulation crumbling off of it. so I need to rewire the whole engine. does anyone have a wiring schematic for one of these they could share? Serial number is 5190360 if that helps. Thanks for any info.
 

Chris1956

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The max rules web site will have the wiring diagram. That motor has 1 coil and a distributor, correct? If so, the wiring is the same as on the 1977 and earlier Merc IL 6 motors, although the wire colors may be different.

Engine wiring harnesses are available at many web sites. Pick out one for a good price. Ign components are real expensive, so don't screw it up, if you rewire it yourself.
 

Chris1956

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Actually, I think the change-over from Battery-powered CDI to ADi was 1979 1/2. I was too lazy to look up his serial number, however, to see which one he had.
 

James_Ketcham

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well i'm repairing the wires 1 by 1. I've never seen a engine where every wire the insulation just crumbles off. here is the serial number for the engine. 5190360 says it is a 1979 140. today I repaired most of the wiring, but there are hmm a few that were broken and since there is no insulation on them I'm a little leary of just guessing. I did take the starter off as it wouldnt turn and completely rebuilt it, then pulled all the plugs and did compression tests on all 6 cyl and 5 were almost perfectly 125lbs, the bottom cyl though was at 121 lbs. I had the harness unplugged while testing since everything is bare wired. just jumped the starter hot wire to crank it over..

Yes it has a distributor with 3 wires running out of it to a box that is mounted directly in front of the middle carb. no points, no trigger coils under the flywheel, just a distributor with a thin disc under the rotor. I'm sorry I am pretty new to boat engines so i'm not sure of the lingo for the parts.
 

James_Ketcham

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The max rules web site will have the wiring diagram. That motor has 1 coil and a distributor, correct? If so, the wiring is the same as on the 1977 and earlier Merc IL 6 motors, although the wire colors may be different.

Engine wiring harnesses are available at many web sites. Pick out one for a good price. Ign components are real expensive, so don't screw it up, if you rewire it yourself.

yes 1 coil , 1 distributor. not sure what or where the max rules web site is.
 

Chris1956

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Search for the max rules site. It is one word with com after it. The rotor is $200+, very fragile and not removeable. The distributor cap is $200 to replace. Both rarely need replacement. Spark plug wires are avail, but last a real long time.
 

James_Ketcham

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Search for the max rules site. It is one word with com after it. The rotor is $200+, very fragile and not removeable. The distributor cap is $200 to replace. Both rarely need replacement. Spark plug wires are avail, but last a real long time.

Got it thank you.. it's odd the 1979 one is not the same as mine.. had to find the 1400 late model one and it was the same as mine.. but I did good today all the wires have been replaced but 2 inside the engine area. looking at the diagram everything i did was 100% spot on and now i can finish it tomorrow and try to see if it'll run. YAY!
 

Chris1956

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Gee, the 1500 and 1150 motors from 1977 should be the same as yours. Maybe the 140 was from the early 70's?
 

James_Ketcham

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Gee, the 1500 and 1150 motors from 1977 should be the same as yours. Maybe the 140 was from the early 70's?

pretty sure this means it is a 1979. :)
 

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Chris1956

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James, I was referring to the wiring diaghram you were using.

Max rules ought to have two wiring diagrams for the 1979 140HP motor. One for ADI ignition (1979 1/2) and one for Battery-powered CDI (1979), however, they definitely have one for a 1977 Merc 1500/1150 which should match your motor's wiring.

Your 140 was actually a Merc 1500 that had a name change, in 1978 when the Merc 150HPV6 was introduced.

Wire colors changed around 1980 or maybe a bit earlier, so watch out for that.
 

James_Ketcham

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James, I was referring to the wiring diaghram you were using.

Max rules ought to have two wiring diagrams for the 1979 140HP motor. One for ADI ignition (1979 1/2) and one for Battery-powered CDI (1979), however, they definitely have one for a 1977 Merc 1500/1150 which should match your motor's wiring.

Your 140 was actually a Merc 1500 that had a name change, in 1978 when the Merc 150HPV6 was introduced.

Wire colors changed around 1980 or maybe a bit earlier, so watch out for that.

all good here. I thank you for all the information, it is always appreciated. I completed the wiring this morning, triple checking each wire at the plug on the engine. Unfortunately for me it has no spark so now I need to find information on testing the switchbox and distributor. anything could have been wrong with this, the wiring like i said earlier had almost every wired with the insulation crumbling off of it. The previous owner had gooped on silicone sealant to several of the wires. my guess is he saw the wires corroding and perhaps it shorted out the switchbox or disributor. I won't know until i find a service manual that covers this.
 

Chris1956

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The CDI electronics website has a test for your ignition. It assumes the coil is good, which most are. It will test wiring and switchbox. If that passes, the trigger is the prime suspect.
 

James_Ketcham

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The CDI electronics website has a test for your ignition. It assumes the coil is good, which most are. It will test wiring and switchbox. If that passes, the trigger is the prime suspect.

thanks. checked it out and also found a U-tube video on how to test the switchbox and distrib.. all good info. turns out I wired everything 100% and found a ground wire missing from the distrib to the engine block. made one up and now i have plenty of spark.. WOOHOO! one more step closer.. now to go to work on the carbs. thanks again for the info. :D:D:D:joyous:
 

James_Ketcham

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Hey! Great news! finished up battery connections, rolled the engine over and it fired right up and sounded great! it didn't pee in the first 10-15 secs though so I shut it off and tore the impeller out took see what i expected.. it was hard and cracked. got a new one and put it all back together and it was working great on Muffs. :joyous::joyous::joyous: Thanks again for all the info and help and patience. Yes I'm very new to the boating world but i'm getting an education in real time as I plunge into this..
 
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