I have found and installed an original Sun Tach in my 59 GMC with the original 235 I6.
The tach is electronic, and came with the EB7A tranmitter.
I followed the original installation instructions with the tach and the tach needle operates up and down with engine RPM, but I think it is reading to high, ie. more rpm on the tach than on the engine. At idle the tach reads 1100 rpm and driving down the highway at 55 mph (original drivetrain, 235 I6, 3 speed manual, and 3.90 rear end) the tach reads anywhere from 2500 rom to 4200 rpm. When driving at 55 rpm the tach reads fairly consistant, but different each time I drive it.
There does not seem to be much for adjustment on it, just a screw to turn to steady the needle, which I have done.
One problem with the tach is it requires a 1.35 volt mercury battery, which I can not find. So it now has a 1.5 volt battery.
Any ideas?
