1986 mercruiser shift cutout (interrupter) switch problem

J

Jmcconnell

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Hello, first time post. Thanks for any help in advance. I have a mercruiser 3.0 that I have completely restored.(first timer) I have everything working great except the shift interrupter switch. Engine had old roller switch which which I have replaced with the newer button style. Had to get new shift cable mount plate bc of the old rollers are hard to find new. Long story short. When I discount the new switch the engine starts and shifts fine(out of water). However when I wire up new switch I get no spark. If I press in the switch while someone else starts engine it fires up no problem... I am perplexed as to what is going on. I have looked at wiring diagram and it shows the green white wire leaving the shift interrupter switch and running to the distributor. However my distributor only has a black wire running from it to the negative on the coil. I am missing something...thanks again.
 
Eric 3.7LX Alpha 1

Eric 3.7LX Alpha 1

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Jmcconnell said:
Hello, first time post. Thanks for any help in advance. I have a mercruiser 3.0 that I have completely restored.(first timer) I have everything working great except the shift interrupter switch. Engine had old roller switch which which I have replaced with the newer button style. Had to get new shift cable mount plate bc of the old rollers are hard to find new. Long story short. When I discount the new switch the engine starts and shifts fine(out of water). However when I wire up new switch I get no spark. If I press in the switch while someone else starts engine it fires up no problem... I am perplexed as to what is going on. I have looked at wiring diagram and it shows the green white wire leaving the shift interrupter switch and running to the distributor. However my distributor only has a black wire running from it to the negative on the coil. I am missing something...thanks again.
Click to expand...
Sounds like a points ignition.

The White/Green wire should be connected to the (-) on the coil not the distributor. The only other wires on the (-) on the coil would be a grey colored wire which would be the sender wire for tach if you had one. (It should not be grounded), and the Black wire that runs to the distributor.

When the shift interrupter activates, it moves off center, and pushes in on the switch, which internally touches the white/green wire to the black wire (both connected to the switch), which grounds (-) on the coil killing spark.
If the white/green wire has continuity to ground with the cut off switch centered there is a problem. Follow the wiring and make sure the White/Green wire isn't bare anywhere along it's run where it could be touching the engine and grounding itself.

You can test the switch for continuity between the two wires using a digital multi meter or test light.
 
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Jmcconnell

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Eric 3.7LX Alpha 1 said:
Sounds like a points ignition.

The White/Green wire should be connected to the (-) on the coil not the distributor. The only other wires on the (-) on the coil would be a grey colored wire which would be the sender wire for tach if you had one. (It should not be grounded), and the Black wire that runs to the distributor.

When the shift interrupter activates, it moves off center, and pushes in on the switch, which internally touches the white/green wire to the black wire (both connected to the switch), which grounds (-) on the coil killing spark.
If the white/green wire has continuity to ground with the cut off switch centered there is a problem. Follow the wiring and make sure the White/Green wire isn't bare anywhere along it's run where it could be touching the engine and grounding itself.

You can test the switch for continuity between the two wires using a digital multi meter or test light.
Click to expand...
Thank you for the follow up. I will check over the wires again!
 
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Jmcconnell

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Meames1 said:
Where did you source the switch? Sounds like you have a NC (normally closed ) switch. It should be a NO (normally open) switch.
Click to expand...
I was given 2 cutout switch from a mechanic friend. Both are doing the same thing. Do they even sell mercruiser cutout switches that are NC?
 
achris

achris

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"Mercruiser 3.0" isn't much help. They have been producing the 3 litre since the ark (I think Noah had a twin set up).... Give us a year (of the engine NOT the boat!) or better, a serial number.

Without knowing which 3 litre, here's a circus diagram of my best guess.

1625134722108.png
 
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Jmcconnell

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achris said:
"Mercruiser 3.0" isn't much help. They have been producing the 3 litre since the ark (I think Noah has a twin set up).... Give us a year (of the engine NOT the boat!) or better, a serial number.

Without knowing which 3 litre, here's a circus diagram of my best guess.

View attachment 344327
Click to expand...
Thank you for this! This looks closer to my wiring!!! When I get home I will get the engine serial #. Only difference I see in this diagram Vs what’s on my engine is I have a green/white wiring coming out of harness near the starter and cut out switch area.
 
J

Jmcconnell

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Jmcconnell said:
Thank you for this! This looks closer to my wiring!!! When I get home I will get the engine serial #. Only difference I see in this diagram Vs what’s on my engine is I have a green/white wiring coming out of harness near the starter and cut out switch area.
Click to expand...
also I see where white/green goes into harness but doesn’t come out. I bet previous owner had to splice it with a different color wire. Think I am going to have to remove electrical tape around harness and start following wires! Thanks again!
 
Bondo

Bondo

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Jmcconnell said:
I was given 2 cutout switch from a mechanic friend. Both are doing the same thing. Do they even sell mercruiser cutout switches that are NC?
Click to expand...
Ayuh,..... The older style are NO, 'n the newer style are NC,....
 
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