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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10899
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1973 Mercury 40hp outboard that is pull start, not

Customer Question

I have a 1973 Mercury 40hp outboard that is pull start, not electric start. I am not getting spark and would like to know where to look and what to test to find my problem.
Submitted: 12 days ago.
Category: Boat
Expert:  Tan replied 12 days ago.

Hello, I'm Tan. Welcome to JustAnswer. I'm reviewing your question and will reply momentarily.

Expert:  Tan replied 12 days ago.

Could I get the engine serial number please?

Customer: replied 12 days ago.
Expert:  Tan replied 12 days ago.

ok got to the switch box and disconnect the salmon colored wire.The switch box is the one that the ignition coil green wires connect to.

Customer: replied 12 days ago.
Ok. Sorry took so long. I was away from motor. Now I can look directly at it. I disconnected the salmon wire from the switchbox.
Expert:  Tan replied 12 days ago.

Do you have spark? If yes then you have a bad stop switch or tilt switch.

If no then we have to test the stator and the trigger voltage outputs to the switch box. This will require a peak reading volt meter or DVA adapter to do these tests.

Customer: replied 12 days ago.
What do I do next?
Expert:  Tan replied 12 days ago.

Do you have spark? Do you have a spark gap tester to check spark at the spark plugs?

If yes then you have a bad stop switch or tilt switch.

If no then we have to test the stator and the trigger voltage outputs to the switch box. This will require a peak reading volt meter or DVA adapter to do these tests.

Customer: replied 12 days ago.
No spark
Expert:  Tan replied 12 days ago.

If no then we have to test the stator and the trigger voltage outputs to the switch box. This will require a peak reading volt meter or DVA adapter to do these tests.

Do you have either of these?

Customer: replied 12 days ago.
I have a gap tester and I don't get any spark jumping even a 1/16 of a gap
Expert:  Tan replied 12 days ago.
If no then we have to test the stator and the trigger voltage outputs to the switch box. This will require a peak reading volt meter or DVA adapter to do these tests.Do you have either of these?
Customer: replied 12 days ago.
I have a multi meter
Customer: replied 12 days ago.
Which do you want me to test first?
Customer: replied 12 days ago.
Does it need to be analog?
Expert:  Tan replied 12 days ago.

No you can use the DVA adapter with a digital meter.

The green wire coming from the stator to ground. Disconnect the greem wire from the switch coming from the stator.Crank the engine what is your voltage reading.

Customer: replied 12 days ago.
Green wire from the coil?
Expert:  Tan replied 12 days ago.

Did you read my last statement?

Customer: replied 12 days ago.
I have a blue and a red wire
Customer: replied 12 days ago.
I have a wire that comes from the coil back to ground.
Customer: replied 12 days ago.
I don't see any ground wire from the stator, only the blue and red wires.
Customer: replied 12 days ago.
Do I need to reconnect the salmon wire? Or do I leave disconnected?
Customer: replied 12 days ago.
Across the front of my switchbox, I have orange, salmon, white, red, blue wires. The green wires are the ones on either side of the switchbox.
Customer: replied 12 days ago.
That order is if you look from front of motor, left to right.
Expert:  Tan replied 12 days ago.

Ok test the red wire to ground then the blue wire to ground. These wires need to be disconnected for this test. This is a cranking test.

Customer: replied 12 days ago.
Hello?
Customer: replied 12 days ago.
Ok. Delay in responses. Sorry
Customer: replied 12 days ago.
Disconnect the red and test to ground? Then reconnect and do same with the blue wire?
Expert:  Tan replied 12 days ago.

Correct. These are peak voltage readings.

The site is having issues moving real slow. So bear with me.

Customer: replied 12 days ago.
Ok
Expert:  Tan replied 12 days ago.

Keep me posted to your findings.

I hope I’ve provided the information you were seeking. If you are happy with my service, your 5-star rating at this time is most welcome. If you need more help, please let me know so l can continue to assist you.

Customer: replied 12 days ago.
53 on the red, 9.2 on the blue
Expert:  Tan replied 12 days ago.

What meter are you using? Peak reading or the DVA adapter.

A standard multi meter will not read correctly.

Customer: replied 12 days ago.
I will have to find a new dva. Mine must be broken.
Customer: replied 12 days ago.
But I will have to wait to get it. I don't have a store around me readily available with one on the shelf. Ordering one will take a week to get it. I will have to continue after I get it.
Customer: replied 12 days ago.
What should I be looking for within range for those wires?
Expert:  Tan replied 12 days ago.

Blue to engine ground. 180-400 peak volts and Red to engine ground 25-100 peak volts.

Then you want to test the trigger wires brown to white 0.5+ peak volts. All these test are done wires disconnected and cranking the engine.

If these test good then you have a bad switch box.

Follow up questions are always welcome.

Thank you......Tan

I hope I’ve provided the information you were seeking. If you are happy with my service, your 5-star rating at this time is most welcome. If you need more help, please let me know so l can continue to assist you.

Customer: replied 12 days ago.
Ok. Thank you for the info. I will get back to you with any other questions.
Expert:  Tan replied 12 days ago.

Your welcome.............Thank you..............Tan

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