Hi, I bought a 74 corvette which someone converted over to HEI, and had the tach converted to electric, however, the tach is not working. the needle moves to 900 RPM when you turn the key on, but doesn't give any movement.
I've pulled the dash apart and checked the wire going to the TACH lead on the HEI, (and it shocked me at the tach, so I know its getting a good signal!). For this converted tach, should I just order a 75-77 circuit board from zip or ecklers? Will that board have the same sweep and degree readings as my 74' face? Thanks.

 

I just purchased a converted tach for my 72 from www.corvetteinstruments.com I am sure he would have an answer for you. very nice to deal with.

 

Stephen; since the needle moves upon power-up... I'd look elsewhere for the problem.

Follow the tachometer lead from the HEI all the way to the back of the tachometer. You might find an inline filter somewhere along the way. These tend to go bad. You can bypass the filter and try to see if the tach will register RPM changes.
If you don't find an inline filter, then this may of been what caused the coverted tach to fail.

Upon power-up, the needle should go to zero. Assuming your tachometer and circuit board are OK, you can reset the zero by pulling the needle and placing it back on at the zero mark (with the tach powered).

I would not buy a board from Ecklers. If I remember, they're selling the Wilcox board which IMO is problematic.

If you purchase a new circuit board, then I'd suggest buying one from J. Gardner 610-797-4048

yes, almost exact but not quite 100% If you convert a mechanical 68-74 tach over to electronic, and use the same dialface (which is exactly what I do), then I place the pointer one graduation just-barely on the minus side of Zero; and then I calibrtae for midrange and redline RPM.

 

There was just a wire going from the HEI to a sun super tach on the column (the previous owner obviously didn't want to deal with it). I want the original gauge to work for appearances sake, so when I pulled apart the dash to hook it up I found out it was converted to electric already. When I applied power to the two terminal that are marked by the converter as power and ground, the gauge does "zero" at around 900 (I remember my 77' did this if you turned the key on without starting), but when I hooked up the tach lead that goes straight to the HEI's TACH connector, it does nothing.
I have now got a strange problem in that my oil gauge doesn't work unless the tach lead is hooked up to the sun supertach, it will sit at zero unless that's connected (hooking it to the converted one doesn't make it work), WTF??????

 

with all of that going on, check for loose/missing grounds.