Tach and Speedo Trouble

Looking for some guidance regarding a sporadically inoperative tach and speedo. They are inoperative independently from each other in that the problem doesn't occur between the two gauges simultaneously. So far we checked the speed sensor at the trans-axle, which was loose. We tightened it up but the problem is no better. We then checked for the tach signal wire connection at the coil and found it to be good. My next step would be to remove the gauges and check input signals to determine if the problem is wiring or the gauges themselves. When they're working, the do so accurately and smoothly. Let me know if I'm on the right track or if you have any other suggestions.

Thanks,

Tyler

 

Just to update as both issues have been resolved. The tach problem was due to a faulty voltage regulator that was causing the alternator to over-charge. The speedo was a ground issue with the sensor at the gearbox. Removed it to take it apart and check diodes and found the ground wasn't making good contact with the circuit board. Viola!