1971 Mercury 800 80hp Switchbox...

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cupprof

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May 10, 2013
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My motor died the first day out this spring... it just stopped while it was running great at full speed, and now won't start and the plugs have no spark. My mechanic is no longer a mechanic, so I'm struggling to solve the problem with no experience and essentially no mechanical ability. I've been told the problem is likely the switchbox, so I'm willing to work on it.

Here's my dilemma... My switchbox looks like this:
my switchbox.jpg​

A used switchbox for my motor on ebay looks like this:
switchbox.jpg​

Why do they look so different? Is that not really my switchbox, did I take off something else?

Thanks in advance for your advice,
~ John
 
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carholme

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Re: 1971 Mercury 800 80hp Switchbox...

Is this a six or four cylinder?

Gerry
 
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cupprof

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Re: 1971 Mercury 800 80hp Switchbox...

It's a 4 cyl. Sorry I didn't include that.
 
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carholme

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Re: 1971 Mercury 800 80hp Switchbox...

So it is a 1971, using the s/n 3144866, you discussed in your previous posts.

80 1971 E S&L 2986444 - 3186282

From here:

MERCURY OUTBOARD MODEL YEAR GUIDE 60 HP - 100 HP -- Mastertech Marine

Parts List:

MERC 800E - Mercury, Mercruiser, Force, etc. Parts Lookup

See switchbox as item 1 under STARTER MOTOR AND WIRING HARNESS.

You should always use the correct part numbers to identify the parts. Do you have the p/ns from the switchboxes you have and did you actually do any tests to determine if you should order one?

Gerry
 
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cupprof

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Re: 1971 Mercury 800 80hp Switchbox...

Thank you! At first i didn't recognize the p/n, but now see it as 337-4411.

I have a CDM 3 Multimeter, but that's the extent of my equipment and unsure what to test. I just figured I'm smart enough to start replacing stuff and hopefully I'll find the right part.

I sure appreciate your help!
 
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cupprof

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Re: 1971 Mercury 800 80hp Switchbox...

Thanks. I read another document from CDI which explained how to test it. But that document also mentioned that the 337-4411 should be converted over to a 332-2986/393-3736 type system. The 332-2986 switchbox is the one I found on ebay, but it has 4 connections on one side and black/white/brown connections on the other side. Wonder what those 3 connections are for?

Thanks for your help!
 
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Moody Blue

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Re: 1971 Mercury 800 80hp Switchbox...

I've got three of those 71 Merc 800 motors and none of them had a switchbox like the one you show in your photo. All three of mine look like the photo from the ebay listing. Four terminals on one side (red, white, green, brown) and three terminals on the opposite side (black, white, brown). The three terminals connect to the trigger circuit in the distributor.

How is your existing switchbox connected?

Taking a step back for a moment, why are you assuming the switchbox is bad? Replacing parts untill you find the "bad" one can get real expensive, real fast, especially on these old motors. Could be a number of things that would be cause for no-spark.
 
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cupprof

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Re: 1971 Mercury 800 80hp Switchbox...

Moody Blue said:
I've got three of those 71 Merc 800 motors and none of them had a switchbox like the one you show in your photo. All three of mine look like the photo from the ebay listing. Four terminals on one side (red, white, green, brown) and three terminals on the opposite side (black, white, brown). The three terminals connect to the trigger circuit in the distributor.

How is your existing switchbox connected?

Taking a step back for a moment, why are you assuming the switchbox is bad? Replacing parts untill you find the "bad" one can get real expensive, real fast, especially on these old motors. Could be a number of things that would be cause for no-spark.
Click to expand...

I appreciate your time, Moody Blue. I'm really clueless, but trying to learn. My switchbox has a Green wire that goes to the coil, a brown wire that goes back to the console (tach? which I don't have), a blue wire that goes to the distributor, and a red wire that goes to the battery. There are no other connections on my switchbox.

I am only assuming the switchbox is bad because many of the wires were bare with the insulation dry-rotted and brittle and because my former mechanic said that was the likely problem.
 
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emckelvy

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Re: 1971 Mercury 800 80hp Switchbox...

Attached is the correct wiring diagram for your motor and a couple of pics of the trigger assy, HTH.............ed
 

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  • M800 Weird Ign_ Wiring Diagram.jpg
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  • M800 Weird Trigger Ign_1.JPG
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  • M800 Weird Trigger Ign_2.JPG
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Faztbullet

Faztbullet

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Re: 1971 Mercury 800 80hp Switchbox...

Yep that used on the old horseshoe triggers.....
 
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emckelvy

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Re: 1971 Mercury 800 80hp Switchbox...

Ok, just a little more analysis, if you look at the diagram I posted, you'll see that the "Mercury" switch can short out the ign to kill it. Normally this would only happen if the motor hit an underwater obstruction and tilted up. But it is something that could easily be disconnected to rule it out.

On page 276 of the manual linked in a previous posting, the section applicable to your ign is titled, "WIRING AND CONNECTION TEST
(Model 800 Ser. No. 3051041 through 3052380 and Model 800 Ser. No. 3144219 through 3192962 ONLY)".

Before you start testing, line up the flywheel timing marks so #1 piston is at Top Dead Center. Then stick a spark plug in the #1 plug wire, and ground the shell of the spark plug to the engine block.

This ign requires constant power on the red wire connected to the switchbox, and switched power to the white distributor wire, which is connected via a terminal block to the main wiring harness. The white wire is powered up with the ign switch in "On" or "Start".

Switch the ign to "On" and check that you have 12V on the white wire to ground. Also be sure there is power on the switchbox red-wire's terminal. Fix any problems found here, before proceeding with testing/troubleshooting.

Next, disconnect the blue wire(s) off the switchbox and turn the key to "On". With a wire connected on one end to a solid engine ground, use that wire to momentarily ground the blue terminal on the switchbox. Every time you ground/unground the terminal, there should be a sparkl.

If you have spark for this part of the test, but no spark when the dist is hooked up and the motor is cranked over, it indicates a bad trigger assy in the distributor.

If you don't have spark, it doesn't specifically rule out a problem with the distributor, but it does point to a problem with switchbox or coil. Since the Merc ign coils are the least likely component to fail, in that case I'd say the switchbox would be bad.

One thought, you said the wiring was in bad shape, has this been repaired? Bad wiring in itself can cause ignition failure. All the wiring & connections need to be up-to-snuff before even bothering to test components.

HTH & let us know what you find..............ed
 
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