Tachometer re-wiring (6-cyl to 8 cyl)?

[Ghost]

Curious if anyone knows how I can re-wire a tach so it works with an 8 cylinder motor, if that is even possible.

The context is that before, I had twin inline 6 motors in the boat. Now I have a single v-8. Until I do a whole new dash project some ways down the road, I'm trying to make use of gauges I already have. For the most part I have pairs of gauges from the twins, but will be happy to have one from each pair hooked up and functional.

I know that many tachs are adjustable to work with 4, 6, or 8 cylinder motors. I don't know if mine are, but I suspect they might be. They are old 70's vintage Kiekhaefer Mercury tachs. Here are pics of the front and back.

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In the second pic, I've labeled 4 terminals A-D. Two are connected (to purple wires and a gray wire). Two are not connected. I'm wondering if anyone is familiar with these, and knows whether some re-arrangement of wiring will/might run the tach properly for a V-8. (I tried a couple things already that didn't *seem* right, and figured it might be worth asking now instead of blindly dowsing for accurate rpm.)

All thoughts/speculation/vague-distant-recollection welcome. Thanks in advance,

Mike

[BOSTONCAMARO]

some early Sun and SW tachs, perhaps others had trasmitters, that would vary on what motor they were being run on...

I would bet, yours may not be able to be rewired, maybe shop ebay, the hamb for a 'correct looking' vintage style tach for your boat....

regards, Tim

[BOSTONCAMARO]

....in fact, knowing they are 6 cylinder tachs, you could likely get 50 -75 each for them on the hamb as a lot of guys are running inline 6's in vintage period correct cars and many guys LOVE running marine speed equipment in their cars...as that was also done back in the day

[Just Say N20]

Mike, is 5K enough range for the new engine?

I will see if I can "dig up" the same style tach for a V8 that maybe goes to 6K.

[Ghost]

Tim, thanks much, that's useful info.

Bill, yes, 5k would do as that's ideally where it'd top out with 1 person, 1/4 tank, light chop, etc. I suppose 6k is probably the perfect gauge but 5 would be fine. Seen some that were similar but outboard-only on eBay. Thanks much for looking but please don't beat yourself up trying. It's no sweat if I can't re-wire to make mine work or if one cannot be found since I expect to do a new-dash project sometime anyhow. If I have to buy a new tach now, it only means deciding on a style and springing for some of that HW a bit early. (Though I suppose with the right gauge, I'd be tempted to re-do the dash with (half of) all the original stuff.) Many thanks,

Mike