Roadsters & Ragtops
"… the Smiths electric tachometer, the tach was not able to read the pulses at all the current sensing loop is not able to properly read the higher current coming from the coil, the resistance in the pick-up wiring is too low for the sensor. To retain the original gauge and restore function required an electronic modification to the tach.” Courtesy of Ragtops & Roadsters
link to the article