As you see so often in here, the tachs on our cars are often inaccurate. The fix is in these threads.
https://www.thirdgen.org/forums/elec...ht=91+tach+fix
https://www.thirdgen.org/forums/elec...ht=91+tach+fix
The V8 tachs call for 192-200 k-ohm resistors, the most common being 196k. I have bought some 196k +/- 1%, 1/2 watt resistors, blue bodied which is the fire resistant used most often in automotive applications. This is a single resistor, eliminating the need to solder ones in series, adding to the clutter and more variables with +/- tolerances. All the ones I have tested with my DVO meter read between 194.2- 194.9k, roughly -1% or less. I will drop one in the mail to you for $1.50,(testing it first) which is cheaper than the gas to run around and try to find one. I am not making much on this if anything at all by the time you figure in a 46c stamp, envelopes, and the initial cost I have for the part. Just doing this to make this repair easier for members, but not willing to pay to do so.

Can't get a good pic of things so small for some reason, but the color codes are:
brown = 1
white = 9
blue = 6
orange - 1k multiplier
brown = +/- 1%