Tachometer too high

[Md11hud]

Finally have my 70 R/T running and driving. I wound up replacing the wiring harnesses for the dash and underhood. Got the alternator rebuilt, put in a new voltage regulator and installed the solid state voltage reducer for the gauges. Replaced the ammeter with a Bosch Voltmeter, and ran the alternator to the battery terminal of the starter relay and added fuse able link. The only problem I am having is the Tach is showing about 2x high. I put a Bosch Tach on to check and it is showing RPMS in line with what I am hearing from the engine. This car was only run for ten years, then stored. It did have obvious electrical problems judging from the melted firewall connectors, and the fried fuel gauge. Anybody have experience with the OEM tach giving bad readings? Can they be rebuilt, or should I just buy a new one.

Mike

 

[Chryco Psycho]

I have rebuilt a number of factory tachs , there is a newer electronic conversion circuit board that is easy to install ,
You should by the signal generator with it to properly calibrate the tach

 

[Chryco Psycho]

The kit I used was made by RTE [Real time engineering]

 

[moparleo]

https://www.rt-eng.com/rte/images/c/ce/M5tachboard_manual.pdf