Is it possible to run two Tachs at the same time?

Posted By: stan1970

Is it possible to run two Tachs at the same time? - 08/17/08 12:32 AM

I suspect the Sun tach (looks to be somewhat old) in my 1970 Coronet is not reading accurately at higher RPMs. "Feels" like it's ok at idle or low RPMs. I've heard that some older tach have problems with Mopar electronic ignition, so I'm not sure if this is a factor.

I was wondering if it would be possible to have two tachs running a car simultaneously?? From what I remember, a tach gets it's info from the negative side of the coil, right? If I had another tach and powered it from the right source and added it's wire to the one from the Sun tach at the coil now, would that work?

Thanks a lot!

--Stan

Posted By: stumpy

Re: Is it possible to run two Tachs at the same time? - 08/17/08 12:37 AM

I don't see why it wouldn't work.

Posted By: JohnRR

Re: Is it possible to run two Tachs at the same time? - 08/17/08 12:44 AM

yes i have , tic toc tach and a stewart warner , but with points .

Posted By: moparcanuk

Re: Is it possible to run two Tachs at the same time? - 08/17/08 12:51 AM

I've run a factory tach and Dixco tach at the same with points and also with electronic ignition.

Posted By: Magnum

Re: Is it possible to run two Tachs at the same time? - 08/17/08 12:51 AM

I've seen factory and aftermarket tach running together many times. 2 aftermarket ones can't see why not but I've never seen it.

Do you have a timing light with a tach?

Posted By: stan1970

Re: Is it possible to run two Tachs at the same time? - 08/17/08 02:21 AM

Thanks all for your answers!

Regarding Timing light -- I just have a basic one -- no tach on it.

I suspect my old Sun tach is not accurate at higher RPMs, so wanted to hook up another to verify before yanking it out and discarding it. When I take off in the car (4speed w/ 4.10 gears in the rear), it feels like it's revving very high and I have to shift, but generally the tach is showing less than 2000 RPMs. So, I figured that can't be right..

So, it sounds like I can have two wires going to the negative side of the coil for the two tachs. I was just thinking that somehow they might interfere with each other, but it sounds like a lot of folks run this way already.

Thanks !

Posted By: That AMC Guy

Re: Is it possible to run two Tachs at the same time? - 08/17/08 02:46 AM

Tone Generators are great for this kind of thing. Every pulse sensing tach can be re-set correctly using a pulse generator.

Believe it or not, anybody with an audio editing program and a line out jack can create their own tone generator

Very helpful when recalibrating old tachs.

Posted By: Dart 340

Re: Is it possible to run two Tachs at the same time? - 08/17/08 02:55 AM

Yes, it will work fine.

Posted By: Anonymous

Re: Is it possible to run two Tachs at the same time? - 08/17/08 03:01 AM

Quote:

Tone Generators are great for this kind of thing. Every pulse sensing tach can be re-set correctly using a pulse generator.

Believe it or not, anybody with an audio editing program and a line out jack can create their own tone generator Very helpful when recalibrating old tachs.

(Ahem...) My age is showing. In the mid '60's I build an Allied Radio "Knight kit" tach, and they had you calibrate it using a high value resistor off the AC line as a pulse source. Nowadays, that would be a gigantic liability.

I would suspect that if you hooked ENOUGH tachs up all the same time, you'll eventally load down the ignition, but I doubt two of 'em will do it

Posted By: DirectSubjection

Re: Is it possible to run two Tachs at the same time? - 08/17/08 03:05 AM

I have one in my dash for driving and one under the hood of my Duster for tuning, both wired to my MSD's tach terminal.

Posted By: sixpack4spd

Re: Is it possible to run two Tachs at the same time? - 08/17/08 05:14 PM

Quote:

When I take off in the car (4speed w/ 4.10 gears in the rear), it feels like it's revving very high and I have to shift, but generally the tach is showing less than 2000 RPMs.

What does the tach say when you are going 70MPH in 4th gear???

Posted By: DaytonaTurbo

Re: Is it possible to run two Tachs at the same time? - 08/17/08 06:48 PM

Just add the extra one in and splice it in to the feed lines of the old tach. Will work fine.

Posted By: stan1970

Re: Is it possible to run two Tachs at the same time? - 08/18/08 04:25 PM

Thanks all for the help!

sixpack4spd - it shows under 3k RPMs in 4th gear at around that speed... which I don't think can be right...

Posted By: stumpy

Re: Is it possible to run two Tachs at the same time? - 08/18/08 04:43 PM

Punch your #s in here and see what you get. http://vexer.com/68rt/speed.html
Figure your tire diameter here. http://www.procomptires.com/conversionchart.htm

Posted By: cruzin

Re: Is it possible to run two Tachs at the same time? - 08/18/08 04:58 PM

I just ran into the same question a few months back when I went to install a shift light which has a tach too.

I called the manufacturer and was told I could wire it in w/o any affect. Seems to work fine.

Posted By: GomangoCuda

Re: Is it possible to run two Tachs at the same time? - 08/18/08 05:37 PM

Quote:

I suspect the Sun tach (looks to be somewhat old) in my 1970 Coronet is not reading accurately at higher RPMs.

I was wondering if it would be possible to have two tachs running a car simultaneously??

Sun Tachs from the 60's all used a tach adapter box. I don't know what happens if you try to use them without the box. probably doesn't work at all. Chances are your tach isn't that old and it is just bad.

As already stated by several others there is No problem hooking up two tachs.

Posted By: DirectSubjection

Re: Is it possible to run two Tachs at the same time? - 08/18/08 11:55 PM

Quote:

I just ran into the same question a few months back when I went to install a shift light which has a tach too.

I actually have two tachs and two shift lights wired up.