The temp / press gauges in a 67.5 operate via a very primitive pulsating DC
input. The pointer is connected to a thermal strip that changes position
depending on the input voltage. You would think it would be possible to get a
calibration curve based solely on the input voltage but the "wild card" in the
instrument panel on all roadsters (except the very early cars) is the part
everyone refers to as the voltage regulator. The reason I call it the "wild
card" is because it's really not a voltage regulator but simply another
thermal
strip that runs the input voltage through a set of contacts which in turn
provides the pulsating DC. Bottom line......The best and most accurate way to
calibrate your fuel, temp or oil gauges is to hook the gauge up on the bench
along with the "voltage regulator" and then use either a real sending unit or
the applicable resistance values to dial it in.
I know it sounds like a little bit of work but I've done a gauge or two in
my day (some would say not nearly enough but that's another story) and this
really is the way to do it right.
Jon (Bummed I missed Solvang) Frampton
Huntington Beach, Ca
|