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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14299
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have no spark to both plugs on my 1995 25hp Mercury. It will

Customer Question

I have no spark to both plugs on my 1995 25hp Mercury. It will spark a few times for the first few pulls but then nothing
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** I will be helping you today. All Mercurys are cataloged by serial number, can I get that number. Do you have a quality digital volt/ohm meter and do you know how to take electrical resistance measurements?
Customer: replied 1 year ago.

The serial number is ***** Yes I can get a multimeter but not sure how to take the measurements

Expert:  Jason replied 1 year ago.
I've got the serial. One thing here is I can't teach you how to use a multimeter, that is something you would have to already know on your own. That being said, do you have any specific questions I might be able to answer for you?
Customer: replied 1 year ago.

How do I test the switchbox and stator to see if they are faulty?

Expert:  Jason replied 1 year ago.
There is no test for the switchbox, only the stator. The switchbox you figure out by process of elimination, what you would do is test around it, and if everything else looks good, then replace it. But if the stator is a fail then it is a fail.
Expert:  Jason replied 1 year ago.
Give me a couple of minutes to pull the specs on the stator
Expert:  Jason replied 1 year ago.
Got it. to test the stator you would disconnect it from the switchbox and test it's resistance. Mercury uses 2 different color stators, one is black in color, the other is red.
Expert:  Jason replied 1 year ago.
If you have the black stator, measure between the blue to blue/white wires, specification is 3250 to 3650 ohms. You are allowed about a 20% variance, so as long as you are within that ballpark, you are okay. If you are not close, or there is no reading, it's bad.
Expert:  Jason replied 1 year ago.
On the red stator, that uses a white/green and a green/white wires. And you would measure between those 2 wires. Specification is 500 to 700 ohms. Again you get about 20% leeway on the numbers.
Expert:  Jason replied 1 year ago.
Was there anything else I could help you with?
Customer: replied 1 year ago.

What other wires should I test other than the stator to work out if its the switchbox?

Expert:  Jason replied 1 year ago.
You would disconnect the black/yellow wire from the switchbox first and reheck for spark. Have you done that yet?
Customer: replied 1 year ago.

No haven't done that yet I'll give it a go.

Expert:  Jason replied 1 year ago.
You would do that first. The way the engine shuts off is by grounding out that wire through the key switch(if you have one) and kill switch. So you start by disconnecting that. If spark does come back, then the keyswitch or kill switch is bad. If there is no change, then you would go on to test the stator. The stator will either test bad, and it is bad. Or it will test good, leaving the switchbox as the faulty part.

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