tgilligan

Hi Guys,
As if I didn't have enough on my project plate, I want to add a tach to my 70' CS. The dash bezel has a clock blank where nothing is used and I was originally going to try and snag a tic tock tach setup to stay factory but they are hard to come by and expensive. If I end up going with an aftermarket AutoMeter style, I needed some advice.

I have the MSD billet read-to-run dist setup and it has a gray tach wire for the input. The MSD data sheet indicates that wire is a 12v source, here's the text:
TACHOMETER INFORMATION
The MSD Ready-to-Run has a Gray wire that provides a 12 volt square wave, 20° duty cycle tachometer signal that will trigger most tachometers. It is recommended to connect this lead to your tach’s trigger input wire and check its operation. Note that the rpm limiter is extremely accurate and due to the variety of tachometers available, there may be differences in the displayed rpm.

Does that mean that I can use that wire from the MSD as the power and signal lead to the tach? I would default to the IGN spade on my fuse block but I'm already using that for the lead to the MSD distributor. If I need to tie into a keyed source, I added a keyed source to my oil sending unit to convert my hot air choke to electric, maybe I could tap into that?

oldcutlass

The gray wire as described from the distributor is your tach signal wire. You will still need a key on voltage supply, ground, and lighting wires.

tgilligan

RandyS

The auto parts stores sell a little adapter that allows you to stack 2 terminals off of one output.

oldcutlass

You have to watch how much load you put on the ignition terminal at the fuse box.

RandyS

True, but a tach draws almost nothing.

oldcutlass

True but an ignition system draws quite a bit.

tgilligan

RandyS

Yes, it should be.