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Whitecap36, Marine Technician
Category: Boat
Satisfied Customers: 1545
Experience:  28 years Certified Marine Technician and past FL State Certified teaching degree
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I have a 1971 Mercury outboard 80 hp 800 Thunderbolt serial

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I have a 1971 Mercury outboard 80 hp 800 Thunderbolt serial #3188614. It stopped running no spark compression is very good motor ran great. Boat mechanic says to replace the Switch Box, Trigger and Rotor. Is it necessary to replace all or can I try just the switch box. If other parts are bad will they damage the newly installed switch box. It seams to me the mechanic just wants to throw parts at it unnecessarily. Any help would be greatly appreciated.

Thank you
Hello, I'm Mike.
I'm happy to help you today. Please post back to this thread for any questions or concerns, either before or after payment.
Yes i agree you have a mechanic that is likely not very familiar with this ignition system. I've worked on many over the years but they have been far a few between lately.
The most common problem in my opinion would be the mercury switch,grounded kill circuit or bad trigger. The rotor although may become loose with improper removal will generally no cause a no spark problem and the switch boxes although easy to replace are hardly ever the case either.
I think your two options are either to find another mechanic familiar with this system and troubleshooting process or attempt it yourself. I must be clear that this job of replacing the trigger (distributor assembly) on a scale of 1-10 is probably a 8-9.
Here is a web address to a 3 page work sheet including a bit troubleshooting that could help. This is a system that could require special tools to complete the troublehooting process.

I hope I've given you the help you were looking for.
Best of luck,
Customer: replied 6 years ago.

Thanks for the reply. I did not mention that the mechanic said that the switch box had power in but no power out. I don't know if that makes a difference or if the mercury switch or bad trigger could cause that to happen. I look forward to your reply.


Thank you


Yes, there will be no power out if in fact the kill circuit is grounded or if the trigger(distributor housing) is bad.
I would follow the short troubleshooting guide I sent you to see if you can determine without special tools if this is the case.
Customer: replied 6 years ago.

One other question I hope. I have the top and front Motor brace that houses the switch box, coil and rectifier off also I have the engine internal wire harness out. The harness is shot so it makes it impractical to test any components without the new harness. I would like to order all parts that I may need at one time. So as I mentioned in my first question if I replace the switch box and coil (they come as one unit from CDI) mercury switch and wire harness could the newly installed switch box get damaged if the trigger is bad. I'm assuming the trigger if bad is shorted out. I sure would like to avoid replacing the trigger as it make no sense at that point not to replace the rotor $200.00 plus and the timing belt $30.00 plus (labor $300.00 estimate from mechanic).Even though I'm a fairly good mechanic (cars) replacing the distributor on this engine is a job I would not want to tackle. The switch box original part #337-4411 CDI makes a replacement for that exact part. I added that info because as I'm sure you know Mercury had a few different ignitions for that same engine series and serial numbers.


Thank you


No a bad trigger will not damage a switch box.
Yeah I understand getting the trigger on and off is headache enough not to mention the work it takes to actually replace the housing it's self.
300.00 labor is a good rate if infact he will be going the complete sync and link adjustments when finished.
For sure at least order the wire harness, install before testing further.
Sounds likes you've got the later model blue coil one and not the older big tan bakolite coil.
Best of luck
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