Horacehoare Posted May 8, 2020 Report Share Posted May 8, 2020 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? Cheers Phill Quote Link to post Share on other sites
stuart Posted May 8, 2020 Report Share Posted May 8, 2020 (edited) Possibly a service interval counter, or for a form of cruise control, not original. Stuart. Edited May 8, 2020 by stuart Quote Link to post Share on other sites
Charlie D Posted May 8, 2020 Report Share Posted May 8, 2020 Phill, 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. Charlie. Quote Link to post Share on other sites
Horacehoare Posted May 8, 2020 Author Report Share Posted May 8, 2020 Crickey, very high tech! (for the period) As the car was a basket case when I got it the wiring was missing but still interesting to know what it is, thanks chaps. Phill Quote Link to post Share on other sites
valvebounce Posted May 11, 2020 Report Share Posted May 11, 2020 (edited) They are used to drive these rally meters https://www.brantz.co.uk/products Edited May 11, 2020 by valvebounce Quote Link to post Share on other sites
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