Remove the Cortina tachometer from the shroud.
Disconnect the wires to the tach.
Twist the chrome bezel by hand to unlock and remove. That may be hard to do so lift the tabs slightly to ease movement.
Remove the two or three slotted screws from the back of the tach and remove base cover.
Locate the largest resister on the circuit board ( 150 ohm 1/2 watt - colors: brown/yellow/black ).
Apply an ohm meter across the resistor to check the value. If > 200 ohms replace it.
If ok, then locate a pot that has a slotted adj. screw on top.
Hook up the bare tach to the dash wiring ( lay it on the column under a rag for support )
Connect a timing light or such with an rpm reading to the engine. Start the engine.
Compare the rpm readings from the tach and T/L. Adjust the pot to the reading on the T/L.
Before attaching the casing to the tach. Drill a 1/4" hole in the casing that lines up to the pot.
That way you can adj. the tach with a screw driver without taking it apart.
Most English Ford tachs ( positive or negative grd ) will need adjusting because of age, unless it's new.
Pete
Great article, thanks for sharing it!
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