MSD 8595 and Smith's Tach

Success yesterday! First crank of 427 SO in MKII and engine/cam break in!

Everything seemed to work with exception of Smith's Tach -- never registered.

Am running MSD 8595 connected RED to coil +, orange to Coil -, and a ground. Connected green black wire from tach to to coil -.

Any ideas?

Thanx
Mark

Tach wire should connect to an output on your ignition box. MSD usually uses a grey wire for the tach output? What kind of ignition box are you using?
Chet

Yes, Chet is correct it will be a separate wire or even a spade plug on the unit itself.

CSCHWER said:

Tach wire should connect to an output on your ignition box. MSD usually uses a grey wire for the tach output? What kind of ignition box are you using?
Chet

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The MSD 8595 Mark is using is a "ready-to-run" distributor, hence no box. It has only a ground and the two coil wires for + and - (with + going to +12V as well).

Instructions are here: http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=6442451633

Alan hit the nail on the head wrt the ready to run wires. Question I have is should the green black tach wire be connected to the positive vs the negative coil as I have it currently connected (ie, is the tach a current or volatge tach)?

muttsjet said:

Alan hit the nail on the head wrt the ready to run wires. Question I have is should the green black tach wire be connected to the positive vs the negative coil as I have it currently connected (ie, is the tach a current or volatge tach)?

Click to expand...

It's a voltage tach. It has three wires: +12, ground, and the signal from the tach. A current tach would have +12, ground, current in, and current return wires since the coil current runs through the tach.

BTW, when I turn on the ignition after a short pause my tach needle bounces once. Does yours?

Also, here's a quick test you can do on the tach: disconnect the black/green tach wire from anything else, turn on the ignition, and then tap the tach wire as rapidly as you against a 12V source (like the positive battery post). On mine this causes the needle to jump around into the 2-3,000 RPM range. This tells you at least whether the tach is alive in any sense.