OMC Tach ID

[lotec]

I picked up two identical OMC tachometers that are either NOS or have very little use. (They were in an OMC tach box) I’m guessing they are from the 1970s but can’t find a part number anywhere on them to cross to the parts/accessory books. They do say they are an alternator tachometer so that helps narrow things down a little, but that still leaves open about 4+ different applications. (And I believe if used on the wrong model they will damage the charging system, damage the tach or simply not work)

Any thoughts on what these may fit would be great – It would be cool if one would work on my 1990 Johnson 115 Cross-Flow V-4. Also, is there a simple way to test them? (note: I’m not an electrical engineer, so I do mean simple!)

Any help or thoughts would be appreciated.

[fleetwin]

Art
That tach has the grey lead meant for the alternator output of the 70s OMC outboards. The OMC stern drive tachs were run off the coil.
So, this tach is for the outboard. There is no adjustment on this tach because back in the 70s only the 6 pulse alternators were used on the OMC outboards. So, this tach should work fine on your engine.
Sorry, I don’t know any way of testing the tach, other than connecting it to see if it works. I’m thinking your engine has the water cooled regulator rectifier instead of the plain rectifier, but you could still wire this tach up temporarily on the terminal board where the grey lead is attached, simply ground the other lead. These early tachs did not require a B+ input to operate.

[lotec]

Thanks Don! They are in such nice shape I may try one – thought it would look better on my 1967 Mako than the 1990’s one I have.

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