This sounds like the tach is not properly grounded.
What ground it is seeing, is thru another device, witch
give it some resistance.

                                                Eric

Anthony Hecht wrote:

> Hi,
>
> Can anyone explain to me why this would happen:
> After installing my new tach, I started the engine. The reading was way too
> high (2-3000 or more). So I went in the back and hooked up my tach/dwell
> meter. When the meter was connected in the back, the readings matched up,
> i.e. the tach on the dash dropped to what seems to be a correct reading.
> With the tach/dwell disconnected, the dash tach jumps up.
>
> I've checked the dip switches, they're correct, 1 - On, 2 - Off, 3 - Off. I
> tried fiddling with the potentiometer screw in the back of the tach and I
> was able to bring the reading down a bit, but not able to make it correct.
>
> Thanks..
>
> ---------------------------------------------------
> Anthony Hecht
> '80 Camper "Badunkadunk"
> Somewhere Between Virginia and Tuesday
> http://travelinvan.com
> ---------------------------------------------------