HELP! Operate Tach out of the Dash

I found a thread on here showing how to make the tach work outside of the dash and for some reason I can't find it again. I tried several different search terms to no avail. Can anyone help? The tach in the 245/SBF isn't working and I don't know if it's the tach or the wiring so I'd like to rule out the wiring if I can.

Thanks

Dan

Never mind. It's easier than I thought - just a bit of tracing the circuit board and the correct connectors became obvious. Piece o' cake......

Dan

Care too share a bit about what your issue was?? My tach has stopped working also and I'm pretty sure its the wiring. but where in the wiring???

Sure, BB!

First of all, to hook up the tack out of the dash. Tech tip - you have to plug the dash back in or the car won't run:

So if you look under the tach dial with the tach out you can clearly see that the center connector is for the tach signal (pulse train). This will be either a single or a double 1/4" flat spade connector at the bottom rear of the tach. There is a small round (cylindrical) connector at the lower right of the tach face (look down on the tach face with the numbers right side up) - that's the positive connector. I found that an old set of DVM probes fit right in those round connectors and I just used jumpers from there to battery power. About 180* across the tach face is another one of those round connectors - that's ground. I you're not sure of your connectors trace the circuit on the board starting at the 2 wires soldered in on either side of the tach signal connector - you'll be able to trace them on the printed circuit board. Hook up your power wires (+ and -) and your signal wire from whatever source you use (stock is usually coil -) and you should be ready to troubleshoot your tach.

It turns out that some tech guy at MSD had told me to tie the tach signal into the coil "-". Well, that won't work on this system. Now the MSD 6AL box has a tach signal but it MUST go, unmolested, directly to the EZ-EFI computer. (Evidently this is true for all pre-packaged aftermarket EFI systems). So you can't T off that line to steal the tach signal.

So in my case I tried a bunch of options and finally got a sharper tech at EZ-EFI (F.A.S.T.) and he tipped me off that the injector pulse is proportional to engine speed. I tried that and it worked - sorta. Turns out that that pulse is about maybe 1/4 of engine speed so when I revved the engine up the VDO tach would read about 1,000 RPM and it had to have been at least 4K.

Now my problems are half over - I have a proportional signal but no way to calibrate it. After a lot of hunting I turned up a tach adaptor from Dakota Digital Dash that basically makes any tach work with any pulse train at about $80 + freight. So that's on the way. Hopefully all I have to do is fire up the engine, read the speed on the hand-held calibration unit for the EZ-EFI, and make the two read the same. Wango-Tango - all set (I hope).

Dan