Check the grounding and power connections on your tach and speedo very
carefully... It may be that you're grounding the tach through the speedo
cable housing, which is possible if you don't have the little black
daisy-chain wire that connects the instruments together, also connected to
the metal dash support rail. I've confirmed that the tach works just
perfectly, if you leave out the ground to the tach, dut you have the dash
lights installed. Similar to the problem you had with the taillights, the
tach can then be grounded through the string of dash bulbs. One way to tell
this is happening, is to turn on the panel (dash) lights and see if the tach
suddenly quits.
Otherwise, you're just up against any of the multitude of tach gremlins. Tom
Hall and I supply replacement (or bypass, if you want to be picky) tach
modules that eliminate the old-electronics tach problems, or we'll rebuild
your tach with the module if you don't have the tools to calibrate the tach
afterwards.
Best regards,
Theo
|