Need help wiring tach

[deluxe]

Here is the story:
I bought an unknown tach off of ebay. It's an older style that I thought would look in place in my 76. Here is all the information I have on it:
1) around the face it says: Patent 3005515 Thomas G. Faria Corp. Uncasville Conn. USA A1430-60-8
2) on the back in large ink letters it says 9M5 and 8 CYL
3) There are two wires soldered to the back. Both red but one with a black stripe.

I did what anyone would do and connect the red wire with a black stipe to ground and the other red wire to the negative side of the coil to see if it worked. I have hooked up another tach this way and it worked fine but when I touched the wires to the coil and negative side of the battery the engine nearly died so I stopped and turned here. It was as if I grounded the coil. Here come the questions.

1) Did I ground the coil? Can that happen if the tach is no good?
2) Was I supposed to hook up the tach in the opposite direction? Does that matter?
3) Is there any other way that this could be hooked up? Anything else I can try without problems?

Thanks in advance

 

[DirtDonk]

That's a tough one. Perhaps they're both for power and the ground is through the tach body/mount? IF that's the case, then one wire (maybe the red?) goes to keyed power, and the other (black w/red?) goes to the coild negative.
"Most" tachs have more wires. Ground, Keyed power, Signal, Light. Since yours only has two, either some other wires are missing, or it's like I said above. Because you HAVE to have the Signal (wire to the coil) and Power (to a keyed ignition source). And of course you have to have a ground, but hopefully it's through the case.
Hope that's accurate. I'm only going from guesswork here. You might try to contact Faria since they're still around. Very high quality stuff these days from what I've seen. Don't know if they still make gauges, but they make all sorts of other stuff and I see their name in the PRI magazine all the time. I'll see if I can get any info from a recent ad for you, but try a web search too.
Good luck.

Found it: http://www.faria-instruments.com/

Paul

 

[DirtDonk]

1) Did I ground the coil? Can that happen if the tach is no good?
2) Was I supposed to hook up the tach in the opposite direction? Does that matter?

Sorry, forgot to actually answer your questions! Hah! It's late.
Yes, it can happen if the gauge is bad, but it could happen also because of the way it was hooked up, if those wires are for something else.
If you ground the coil, it won't spark. Grounding is the same signal that your points or module is sending to the coil in the first place, but it pulses it instead of just holding it (as in: ground-break, ground-break, etc.). IF you give it a straight path to ground, no signal is getting to the coil to spark.

You might try doing it in the opposite direction. Don't know if that's right either, but it might be worth a try. I'd check with the manufacturer first though. I think the other wire is for power. Maybe.

Paul

 

[wildbill]

;D ;D ;D Not nowing the tack you have some have senders that go under the hood and the tack is hooked to it and it is wired to the motor. Sun was one of the ones that worked like this. But most tacks will have a green wire to the coil. %) %) %) Bill %)

 

[Broncobowsher]

Some of those early tachs (like the factory ford tachs and the mustang ralley pack and found on some AMC products) would splice in line with the positive power wire to the coil, often replacing the ballest resistor too.

My guess is to run a set of test wires out under the hood and connect the tach in line with the POSITIVE side of the coil. If you have a miss under load then the tach probably has a built in ballest resistor and you should remove the factory one to get the voltage back up to the coil.

As for wiring, my guess is black with red goes to the keyed power, black goes to coil positive. The tach may be grounded through the case, so keep that in mind.

 

[deluxe]

thanks everyone

I am doubting that the tach is grounded by the case. Except the face which is aluminum, the entire tach is plastic. The two wires that come out of the tach are soldered to leads that come out of the plastic and there are no unused leads. If I run the solid red wire to the ignition positive and the red with black stripe wire to the coil positive how can I expect the tach to work ungrounded?
I bought the damn thing for it's looks and now I am wishing I could throw it back :'( ... I have contacted the company that produced it but there hasn't been any return information yet. Thanks again and keep the ideas coming!

 

[airman]

I don't know about your set up but I bet that tach is looking for a power signal from the dizzy. My new HEI has 2 places for wires. One for the keyed 12V and the other that sends a signal to a tach. The signal basically goes every time the rotor makes a contact on the cap. The 2nd wire on the tach would then go to ground. Thats how I bet it would work on mine but I don't know your Bronco wiring. If you look at a wire diagram for like an MSD it has a separate signal that would go to a tach. I bet thats how your gauge works.

 

[Broncobowsher]

Have you tried wiring it in series yet?
I never said the case was the ground, just maybe.
As for the ability to work without a ground, it is possible. The dimmer switch in your house works without a ground, but the power is AC. Then again the cycling of the ignition system makes for AC power as well.
The other possibility is the voltage drop across the ballast resistor is powering the circuit. It is amazing how those electrical engineers come up with stuff.

Don't cry it doesn't work until you try it.

 

[deluxe]

thanks again

I don't have electronic ignition yet so I don't know of this lead off of the distributor. Hopefully the tach doesn't need that but judging my it's age and the docs I have found on the manufacturers website I don't think this is the case. Is there any more ideas? I hate to junk this thing.

 

[70_Steve]

Is there any more ideas? I hate to junk this thing.

D&M Restoration

 

[iwlbcnu]

Faria made alot of the orig early Ford tachs. my Cylone has one and it only has 2 wires and a seperate light. Mine just pluged into the factory wiring but for awhile I had a Sun in there and was able to use the same wires, one was coil - and one was 12v switched. Try emailing petescomet@aol.com he restores alot of tachs and may have the info.