Tach question

[RUFF]

What would make a tach read backwards? Mine idles on 6k and when I rev it up it goes 5,4,3k.

[Monza Harry]

Ruff I can't think of many scenario's that would cause that. If you know what has been done to the car since the tach started to act up, it may be easier to figure out what went wrong. Personally I am willing to bet that during some dash work the tach wiring became reversed. Or less likely I would suspect you have a couple of things going on at once, first I suspect you would have to have a bad ground for the tach, and second you have to have a sort of "short". This is what would be required for power from that "short" which instead of going to ground would be back feeding through the tach and causing it to read backwards. as this scenario would be an odd set of circumstances, and would also have other "side effects", (ie; what ever was being back feed would be working in the off position). Others will chime in with their experiences, and between us you should be able to get a handle on this. Let us know what you find, and Hope I was helpful! Harry