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Hello all, 

There is a small plastic circular item, with electrical terminals attached, fitted to the rear of my TR4 speedo where the cable usually screws in and it has a threaded boss to take the cable so this item is basically between the cable and the speedo (See photo) Can't find any pics/info, any ideas what it might be?




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Possibly a service interval counter, or for a form of cruise control, not original.


Edited by stuart
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It’s an opto-electrical device that sends out pulses in relation to the turns of the speedo cable. Imagine an opto transistor (or what ever they were called) with a light shining into it. There is a revolving disc with holes in it between the transistor and the light source and as the speedo cable turns, so does the disc and so it interrupts the light source and so gives electrical pulses.

Many years ago I designed a digital speedo system that needed some sort of pulsed input and I used exactly the same item.
As Stewart says it could be for one of several aftermarket uses. Are the wires still attached?
If so you could trace them back to see what it is connected to.



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