tachometer wiring

[JPO]

greetings,

I just installed my dashboard after several weeks of wiring work. Then I tried to start it (it previously ran fine) and I got some strange noises from the engine ignition. Since I had everything previously wired but the tach< I figured that was it. After disconnecting the vintage tach provided by FFR (Autometer) everything was okay. The tach has three spade prongs on the back labelled ground, +12v DC and Ignition. I connected the ignition to the tach wire off of the donor (1989 Mustang) harness (I traced it back to pin #11 on one of the dash guage pod plugs. Does anyone have suggestions on what I have screwed up?
Thanks,
JPO

[Wade Chamberlain]

that sounds like it's wired correctly.  What color is the tach wire?  For '89, I think it should be green w/ a yellow stripe.  Some time later, they switched to tan/yellow.  Wonder if there's a problem w/ the gauge that's grounding out (or constant 12V) on that terminal.  Since that wire connects to the trigger side of the coil, a problem w/ the gauge could kill spark.

[JPO]

The wire off of pin #11 is green with a yellow stripe. Would it make any difference if the +12v is switched power or always hot?

[Wade Chamberlain]

It shouldn't make a difference in the operation of the tach or whether or not the engine runs.  However, the intent is for switched power.

[tim-in-oakton]

I can't speak to that gauge, but a poor gauge design could interfere with the ignition if the gauge wasn't powered up.
Are you sure that there are only 3 inputs though - I would have expected a backlight input as well (+12 switched, gnd, input to gauge from ignition, backlight).

[Wade Chamberlain]

autometer usually has complete separate pigtails for the lightbulbs themselves rather than terminals on the back of the gauge.

[JPO]

The light has separate pigtails which I wired separately through my light switch so I can dim them. That aspect works fine. I did wire the +12v terminal through the switched 12v source. I may call autometer to find out if they have had similar problems elsewhere. The tach should work fine on the 1989 ignition which still uses the coil and distributor???

[Wade Chamberlain]

The tach should work fine on the 1989 ignition which still uses the coil and distributor???

yup

[tom of va]

I have to use a tach adapter. My setup is different. MSD ignition, distributor and coil with Smith guages. The adaptor does make a buz but is needed.

[JPO]

I was thinking about jumping straight over to the coil. If I were to try that, does anyone know what wire I should tap coming off the coil? My coil has a plug connector with two wires coming off of it. From there it drops into the engine bay harness. The FFR instrcutions suggest that the tach should be wired to the Coil (-).
Thanks for any thoughts.
JPO

[Wade Chamberlain]

same wire...green/yellow. 

[JPO]

I'll try it this evening and let you know how it works out. Thanks again for lending me your expertise.
JPO

[JPO]

The problem has been corrected. I jumped directly to the coil and the tach is functioning correctly. Thanks to all for the advice.
JPO

[Wade Chamberlain]

that's good news.  Must be a short in the tach wire somewhere between the coil and the dash.