Switch box compatability

[Nebraskan]

Hey guys, think I've found some replacement parts for the engine I'm working on now that I'm back on the farm again and online.

One question I have is the compatibility of a switch box number to mine, they both look exactly the same and I've already looked it up based on this forum posting: https://forums.iboats.com/forum/eng...22-cross-reference-part-number-to-year-models. And when I check my number to the one I want to buy it shows that the CDI replacement (114-2986 CDI) works for both, but doesn't show if the OEM one would be compatible, which I would assume it would be, but I know the CDI replacement is an upgraded unit so just want to double check that it doesn't have some new style that works for more models than the OEM ones before spending the money.

Anyways, here's the part numbers:
Switch Box: 332-2986a21 (mine, 2-stroke, 6 cyl 900 1978)
Switch Box: 332-2986a22 (one for sale)

I'm assuming they are, but the one I'm looking at has a 4 (not sure if that's for stroke or cyl) and 8 v8 on it's sticker with the part number (332-2986a22) and a 1985 date in the box of the sticker. From my understanding, the distributor trigger disk is the only difference and I will still have the 6 cyl original one from mine, but just want to make sure there's not something I'm missing cause these aren't all that cheap.

Thanks again for any help

 

[Nebraskan]

I was able to find photos for the two if that helps

 

[flyingscott]

Take your serial # and look up the switch box. The A suffix usually is how many times it's been updated.

 

[Nebraskan]

OK, I tried the engine serial number I'm working on (serial number: 484-6442, model= 900 series, 2-stroke 90hp, 6 cyl 1978) on multiple sites and it doesn't directly pull up, so I went to the year/model number and found sections that included my serial number USA 4845301 THRU 5299505 found on the mercury marine .com site: https://www.mercurymarine.com/en/us/parts-and-accessories/parts-catalog and the part number matches with my switch box even though the sticker is half gone you can match the last numbers: 332-2986a21.

So the one I want to buy (picture attached in my previous post, part number 332-2986a22), which like you said, I think should be compatible with my current 332-2986a21 switch box, but just want to make sure as I'm not sure if the 4 is in reference to a 4-stroke or a different 4 cyl setup that would operate differently from mine since it also says V8. For my '78 switch box, I know the distributor trigger works for both 4 and 6 cyl 2-stroke engines depending on what distributor trigger disk you use. The distributor trigger housing and opperation is the same minus the 4 or 6 cyl trigger disk you use, but I haven't seen a 8 cyl trigger disk for it. So is the 4/6 cyl setup the same for this model that shows a V8 sticker??

And same thing, when I use that website and type in both switch box numbers, the replacement part for both is the CDI kit #114-2986 but they don't list that the 332-2986a21 switch box and 332-2986a22 switch box are compatibable. I know it should be as simple as A=B, B=C, so A=C. But I frankensteined a case 1816c skid loader ignition a few years back (used an abs sensor off a '91 f-150 for my magnetic trigger, coil off my '65 mustang, aftermarket ignition module (switch box) off a chevy I think it was) where the ignition module only worked cause the aftermarket ignition module was upgraded to cover multiple models and the stock parts couldn't do it. So that's my hangup is that i've seen stuff that on paper should work, but not work in real life... skid loader still runs by the way

I'm about 99% sure it will work, just need that last little bit of certainty before I feel good enough to order if any of you guys that are more familiar with these old beauties had any input.

And I know I still write to much... I just want to cover things and this is how I work things out in my head

 

[flyingscott]

I do not believe Mercury ever made an 8 cylinder outboard. Are you sure the motor is a 1978 model? The parts diagram for your motor only shows a distributor not a switch box.

 

[Nebraskan]

Well crap, that makes it more complicated. I've researched a lot on the '77-79 series and knew there wasn't any in that range. But if you look at the sticker (I'll attach again) on the one I'm looking at it has V8 right on it (unless that means something else like version 8 or something?) and an '85 stamp that could be the manufacturing date not the model year, next to the 4 (again, no idea what that stands for especially if there ain't a v8) it has a small 79 which I guess could be the model year which would put it in my series. It says it's for an 800 merc, but again, the sticker on the back is different then I have seen so that's why I was going off the part number that I haven't been able to cross reference yet minus the CDI part number. I'm attaching a better image of the model that matches mine too (red background)

bah, these stickers are making it worse I think...

 

[Nebraskan]

I do not believe Mercury ever made an 8 cylinder outboard. Are you sure the motor is a 1978 model? The parts diagram for your motor only shows a distributor not a switch box.

and here's the engine badge for this unit and its serial number. it's definitely a '78 with a battery driven ignition system and has a single switch box, distributor, and coil ignition system. Later years went to the power packs from what I've seen, but the first photo with the bad sticker is the switch box I actually pulled off the engine, just unsure about the new switch box I'm looking at as I can't make sense of its sticker or find info on if it is compatible.

 

[Faztbullet]

That box is for the early Mercruiser V-8 engines...Why do you need a switchbox as these rarely fail????