71 Mach 1 - Stock Tach Question

[agraff55]

I have a 1971 Mach 1 with a 351 Cleveland 2V and I am currently installing a new American Auto Wire harness #510662. The car has the original instrument cluster that includes the tachometer. I am also running a stock ignition (stock distributor, stock coil, etc.). I did have to add a ballast resistor to the ignition circuit of the new harness, since I’m running the stock coil and distributor.

The harness includes a COIL/TACH wire that can be connected to the negative terminal on the coil. This wire feeds back to the instrument harness under the dash. The issue I have is that the instructions for the wiring harness state that this wire is only used if you have an aftermarket tachometer. I am wondering if there is any way to make my stock tachometer work with the updated wiring harness and stock ignition? Anyone have any experience with something like this?

 

[Hemikiller]

The stock tach was wired in series between the ignition switch and coil (+). It's a current driven device, in that it measures the pulses of the coil charging and discharging. To use it in it's stock form, you need to splice it into the coil circuit before the ballast resistor.

Your other option is to send it to Rocketman and have him convert it to a modern "3 wire" voltage triggered unit that reads off the coil (-) side.,

https://www.rccinnovations.com/index.php?show=menu-mustang-all#tachs

 

[TheRktmn]

 

[Spike Morelli]

I think MSD still has an adaptor that allows you to do what you want. Years ago, in 1990, I bought my Mach 1. I played around with adding some "hop-up" goodies to the engine, one of which was a Mallory distributor and Hy-Fire box. Well, I never installed the ignition because the instructions said it wasn't compatible with my factory tach. I called Mallory direct to ask for the fix, THEY told me it wasn't going to work as-is, but their competitor, MSD, made an adaptor to allow it to be wired in. Stunned, I asked the phone tech..." you mean to tell me that it's been 20 years since my car was manufactured, and you STILL haven't designed your ignition to work with Ford's flagship performance car? Apparently they hadn't. I called ******** on Mallory for not engineering thoroughly. Brand new, never out of the box, I sold it for .50 cents on the dollar, and installed a Pertronix retrofit in an overhauled replacement distributor, ditched the advance/****** cannister in favor of a simple advance unit as well. I would have liked to use Mallorys unit back then, but..........

 

[agraff55]

Thanks for the help guys! Think I’m gonna go with the MSD tach adapter.

 

[turtle5353]

Send it to rocket man you won’t regret it. Top notch work.

 

[agraff55]

View attachment 70609

Got to looking at your website and changed my mind..... you got a tach (and an amp gauge) coming your way.

 

[70cobrascj]

I have a situation with my set up.
I’m running a Accell electronic conversion on mine and the tach works but it is way off I would say around double or maybe more.
Anyone else experience this.
Thanks

 

[agraff55]

Got my Tach and Voltmeter back from Rocketman today and they look awesome! Can’t wait to get them in the car and operational.

Thanks Rocketman!

 

[c9zx]

+1 on Rocketman's work, top notch. Chuck

 

[agraff55]

Got my Tach and Voltmeter back from Rocketman today and they look awesome! Can’t wait to get them in the car and operational.

Thanks Rocketman!

Got the car running over the weekend. Both the tach and voltmeter work flawlessly... thanks Rocketman!

 

[TheRktmn]

I have a situation with my set up.
I’m running a Accell electronic conversion on mine and the tach works but it is way off I would say around double or maybe more.
Anyone else experience this.
Thanks

I don't have any experience with the Accell ignition system, but did you remove the 'pink' resistor wire?

 

[70cobrascj]

I don't have any experience with the Accell ignition system, but did you remove the 'pink' resistor wire?

No I did not
I power the distributor off the throttle solenoid 12 volt power and the coil is on the resistor wire’s 9 volts.
The Accell is now just like an old Mallory unilite.