Wiring problems Tachometer Mustang -73

[RC92234]

Thanks for the wiring. I got almost the same, only, my doesnt have the small pics that is around yours. 1 question anyhow, I cant read the letters on the small pics. Does it say somewhere any values/numbers for resistors or the tach on the small pics under the wiring diagram?

The only info on the tach is at the bottom on the left of the column of boxes on the right. I took a close-up c-383 and it doesn’t say anything about the resistor, although it’s plainly shown in the diagram.

The repro of this diagram is not the greatest.

 

[Don C]

if you're referring to the resistance through the tachometer, between the two connection points it will be very low, probably less than 1 ohm. The circuit that runs through the tachometer just runs through a set of windings in a transformer that actually works similar to the ignition coil. As the ignition coil is grounded (points close) to load the primary windings the same thing happens to the primary winding in the transformer in the tachometer. When the ground is released (points open) the field that has been generated collapses in both the ignition coil and the tachometer transformer, the ignition coil generating a high voltage pulse and the tachometer transformer generating a low voltage pulse. This low voltage pulse is what the tachometer circuitry converts into an analog signal (voltage) that causes the tachometer needle to move.

If checking the continuity across the two tachometer connections yields a reading of around 1 ohm the primary winding in the coil is OK, if it shows no reading the primary winding or connections to it have failed.

If the primary windings in the transformer have failed the there will also be no voltage passing through the tachometer to the ignition coil and the engine may start when the ignition key is turned to start, but as soon as it returns to the Run position the engine will die.

 

[nursieee]

An update of the tach. and of course some ?????

I took apart the tach and mesured the resistors and the electrical stuff in it.

What happened was when i measured the resistor with my multimeter, which i did set at ohm, the tach needle went to the top. I also put 3 1,5 volt batterys  together and took some wires and put it in to the contact to feed the tach with volts and the orange pin moved about 1-2 mm.

My conclusion here is that the tach works. There must be some other problem than in the tach, i.e the wiring or the ignition coil?, right ?

So for now in waiting for some parts including the tach circuit board from the USA so there will take some weeks before I can install the tach and try my new resistor which is at 100 watts and 1,5 ohm to se if that one will get the tach to work properly.

 

[Don C]

All that you verified is that the windings in the tachometer needle are intact and moves the needle. You did not verify whether or not the circuitry between the input transformer and the needle are functioning. They have to take the pulses generated by the coil (actually the points) and convert them into a steady voltage that then moves the needle. The faster the pulse, the more voltage generated and the higher the needle moves. There are likely a couple of capacitors, an inductor (choke) or two and some other components, like resistor in the circuitry. I haven't seen the inside of one of the original tachometers, so just trying to visualize what components would be required. Old capacitors are the most likely component to fail, although a voltage spike could also take out the inductors. It's also possible that the secondary side of the transformer is bad.

Did you ever measure the resistance between the two wires that connect to the tachometer? If the primary side of the transformer is still good that should measure around 1 ohm.

I'm still not sure that you need to install another resistor. Did you ever measure the resistance (ohms) between the tachometer and the ignition coil? It should measure around 1.5 ohms if there is a resistor someplace in the circuit.

Edit: if you do install another resistor it will get hot, so make sure it is at a location with ventilation and not likely to come into contact with other wires. The normal place for a ballast resistor is at the ignition coil.

 

[nursieee]

Ok ill try to get a better picture to show exactly what i did, but i take it, his does not indicate that the tach is working properly as i thought!

 

[nursieee]

Today i measured every single component on the picture i dont know the name of them but got some resistance in all of them (Ohm).

So that should mean that they are properly working?!

Got the new voltage regulator and the new circuitboard today, ill be back when i got it all together and we will see if the tach will work after that if not ....

 

[Don C]

To accurately measure each component individually requires removing each component from the circuit and test it in accordance with what type of device it is. In the picture I see the a transformer, 2 diodes, a resistor and 2 capacitors, each of which are tested differently. The way to test them in the circuit is to input a signal and then follow the signal through the circuits from beginning to end, and know what the expected readings are after each device. In this case the signal would have to be a pulsing signal, 8 volts loaded through a resistor and unloaded, just like the points load and unload the ignition coil.

 

[nursieee]

Thanx oh, and by the way, broke the tachoneedle today when my 300 USD upgrade for the tach came. Fun. Project now, glue the tachoneedle back in place or glue the whole tachsh**t together....

 

[TheRktmn]

Thanx oh, and by the way, broke the tachoneedle today when my 300 USD upgrade for the tach came. Fun. Project now, glue the tachoneedle back in place or glue the whole tachsh**t together....

Yikes! $300 for a used Faria tach board? I hate to be the bearer of bad news, but you could have bought an entire working tach for less. I'll bet it came from SC....

Gluing the tach pointer on is most likely going to upset the calibration depending on just where the break/repair is. Use as little as possible and use something light - like Super Glue. No epoxy.

The easiest way to test the tach is to find a running car (preferably a Ford product) using points or pertronix ignitor:

1. Remove the wire from the coil + post, connect it to the tach MALE connector (usually a RED wire but Faria ran out of red wire and started using black for both).

2. Run a wire from the tach's FEMALE connector (usually black) to the coil + post.

Start the car.

If it starts, check the tach function.

If it doesn't start the tach board is bad.

If it starts but the tach doesn't work then either the tach board or movement (or both) has failed.

This is for a 67-68 but electrically it is the same:

 

[Don C]

Just curious about what kind of upgrade you are bought, what it is supposed to do?

 

[nursieee]

Just curious about what kind of upgrade you are bought, what it is supposed to do?

Just some new hardware like ignition coil, circuitboard, volt regulator.... just to see if the tach probs had something to do with them....

 

[nursieee]

So now im back on track, it begins again. Some more stupid questions. I gave up my old tach and bought a new one from tachman, that im about to install.

So this is my first question on the picture i point at a device on the wiring schedual is that the one thas called solenoid? On the picture the device that is attached to the blu wire?

 

[Don C]

Yes, that is the starter solenoid, that Ford called a starter motor relay, because that is what a starter solenoid is, a relay.

 

[midlife]

My first time reading this post. 

In 1971, Ford changed the wire color for the "pink" resistor wire to a red/orange or red/green resistor wire. 

 

[nursieee]

More questions.

Nr 1 is wired from ignition coil, same place where the ignition coil goes to the distributor, to the tach.

Nr 2 is where i think im gonna place the red cable from the tach. Can i connect it there or do i have to connect it before the bracket, meaning do have to cut the cable?

Nr 3 I dont find the white device that is connected before the ignition coil on the wiring diagram for my mustang? What is it, why is it there?

 

[TheRktmn]

You are using one of my wiring diagrams (Rocketman) to install a Tachman tach?  Interesting.

The jumper I refer to in my instructions is to connect the two wires in the OEM tach connector to complete the primary circuit from ignition switch to coil +.  I would have sent the original tach pigtail back so that you can use it to make the jumper.

 

[nursieee]

Hi

Yes i bought the tach from you about a year ago didnt have any time to work with it until now, but now im on it again.

I can do that jumper myself with a wire no problem. Since i live in Sweden it takes long time to get things from the USA. Ill get back on how it works.

Now the problem is that white device that is connected before the ignition coil since i dont find it on the original wire diagram? Should i connect the tach to that one or should I connect it direct on the ignition coil ?

 

[TheRktmn]

That white device is an external ballast resistor.  Chances are it was installed for 1 of 2 reasons:

1.  The original resistor wire failed.

2.  They wanted to get 12V for a Pertronix Ignitor or other device, but still needed reduced voltage to the stock coil.

If you are running a Pertonix Ignitor you can power it off the ballast resistor input side (the stud not wired to the coil), and ground it to the block. Note that when using the external ballast resistor you need to run a new non ballasted wire from the ignition switch to the resistor.

(in the future, please try not to give tachman credit for my work) :classic_wink:

 

[nursieee]

Hi

Sorry Rktman, you have to think of me like a sligthly retarded Swede, I will give you credit for your work in the future =)

I still dont really understand how to connect the wire.

By the way it says on my ignition coil that it is to be used with external resistor saw it on the picture, so of course thats why it is there.

It seems like i dont have a pertronix ignitor. So no im still a bit confused. If i follow your wiring Rktman, i conncet the black cable to the block(ground) and the green cable to - on the ignition coil.

But where am i to attach the RED ? on the resistor input (nr 2 in the pic) or direct on the ignition coil + according to your wiring ?

/Conny

 

[Don C]

If you don't have a Pertronix, what kind of ignition do you have? It's important to know what you have to be able to get the wiring correct. Maybe take the cap off the distributor and take a picture of it.