>Modified my tachometer on my '67 MGB to work on negative ground. Now
>it reads 4000RPM at idle and redlines with even the slightest increase
>in real RPM. Have I done something wrong in the rewire ( reversal of
>leads on the "white wire loop" and reversal of resistor and lead to
>voltage and ground points inside the tach)? or can or should this thing
>be recalibrated?
>
This thing can and should be recalibrated. I had a similar problem, but not
quite so extreme. Calibration is a difficult task. First, you need a way
to measure the actual engine speed. I happened to have availability of an
optical tachometer from work. Anyhow, once you establish the way in which
you measure tha actual engine speed, you have to open up the gauge, find the
round rheostat like thing that has a small flat screwdriver fitting on it,
and turn it until the car tach reads the same as the calibration tach. The
hard part is that you can't really pull apart the gauge very well while you
get readings, so it is more or less an adjust, check, adjust, check, procedure.
Phil Bates
58 MGA
67 MGB
75 Jaguar XJ12C
52 MG TD replicar (VW)
86 Peugeot 505 Turbo Gle
86 Honda Accord LX-i
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