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Smiths Rev Counter


Guest Ant

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Hi all,

 

I've got a classic car type smiths rev counter, and I'm unsure of how to wire it in. I believe it may be a current sensing type rather than a voltage sensing one, but I'm not sure.

 

On the dial it says:

 

Smiths, RPM, 4Cyl

 

and in smaller writing underneath:

 

made in UK RVC 2414/OIF 12V negative earth

 

On the back there's a sticker saying "238".

 

It has three connections:

 

1) A spade terminal rivetted to the casing. I reckon this is a safe bet to be a permanent earth, right?

2) An unmarked spade terminal.

3) An unmarked bullet terminal.

 

Both of the unmarked terminals protrude from an insulated pad.

 

The illumination bulb is seperate.

 

Any ideas?

 

Ant

 

PS - I think it's originally from a spitfire, but I'm not sure about that. I have another one, identical only with a black bezel and this one is definitely from a dolomite.

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Hi Ant,

I've got a similar Smiths tacho, but no identifying marks.

You need a switched power feed from the ignition switch,

an earth, and one connection from the LT side of the coil.

I would guess that one is the bullet connector.

 

Should be safe in any case, they both use a +12v supply.

Sounds like you have the -ve connector sussed.

Bob

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I rung an instrument refurbisher in the end to check what goes where:

 

Spade terminal on instrument body - permanent earth.

Spade terminal on insulated pad - Switched positive (eg ignition switch pos 2 output)

Bullet connector on insulated pad - Negative terminal on the coil.

 

Apparently RVC in the codes on the face means that it's a digital tacho, and hence suitable for modern electronic ignition type engines and is voltage driven. (As opposed to the really old current driven types which went in series with the coil).

 

Both of my tachos appear to be working perfectly now ;-)

 

Ant

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