My 68 came with a working 4-cyl Smiths Pod tach. At least it worked fine until I went to an electronic ignition unit. I hooked something up wrong an the Tach ceased to return proper values after I went back to a point-dizzy. It would show what used to be about 1000 rpms as 500 rpms and would not rev beyond 2000 rpms any longer.

I also upgraded to a 140-series Blue Bosch Coil.

I finally found a nice 2" 240-series VDO accessory tach that I installed into my other Smith's Tach Pod. It looks great and I wired it up this afternoon to assist in my carb tuning. Weirdly, this tach also give weird readings. It suggests that my base idle is about 500, when it sounds more like 1500. It revs nicely shooting up to 5000 rpms and higher when I hit the throttle. Still, it's values don't seem right.

It has three connections and all are marked clearly. +, -, and G. + goes to the #1 fused circuit, - goes to the - coil connector, and G is grounded to the same spot as the blower fan.

I tried hooking the + to a different fuse but it does not work at all.

So... do I just happen to have two out o' whack tachs, did I wire this up wrong (I checked the VDO instructions), or is my engine really idling that far off?

Could something else be affecting the signal?