Is It The Auto Gearbox Or What

[azara50]

I have a '97 Carina e cd automatic, occasionally the speedometer stops working and the gears won't change up and the o/d drive starts flashing, then another time it works fine, I've looked for a speedo sensor under the air cleaner, there is nothing there, no electrical wires except the earth cable, its been happening since I had a new brake caliper put on drivers side front wheel as it was seized but I don't think it was that, does anyone know where the speedo sensor is on these models?