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Author
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Topic: 68 tach wiring for dummies?
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Fastback68
Gearhead Posts: 2703
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 12-11-2003 06:41 AM
  
Oh dear, even with my Osborn's wiring diagram, my electrician can't figure this one out. I know he's got it wrong 'cos one thing I've learned is that the tach and the coil should be in series, and he hasn't got it that way.
This is a conversion job. I've got Duraspark electronic ignition, a 12 V coil with a resistor (not sure if I need that) and an 8,000 rpm factory tach.
Could someone give me a dummy version of how the ignition switch, tach and coil relate to each other? Something I can pass on to the elctrician and we'll both understand?
Thanks all!
Simon
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indyphil
Gearhead Posts: 2047
From: Senoia, G.A. USA
Registered: Jul 2002
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posted 12-11-2003 08:15 AM
Simon,
My understanding of tachs is this:
the - side of the coil (thats the one that goes to the distributor) is the side that the tach wire goes to. I say "tach wire" like there is only one, but what i mean is the "trigger" wire. This is the signal the tach uses to know what the revs are. So its not "in series" with the coil. Then the tach will also need a power supply that is "key hot" 12v, and also a lighting circuit supply that dims with the rest of the dash lights.To just get mine working I used the key hot to power the tach and also for the lights, so the lights in the tach come on as soon as I crank the car and get it running. This saved me from finding an appropriate hook up to the lighting circuit. The tach is now the brightest thing in there at night  I made a simple diagram for you but I need to scan it and email to you. unless someone else can articulate it better you might have to wait a little while. ------------------
'68 coupe 289 C code
66 heads, edel 600cfm carb, performer intake, dual exhaust http://www.geocities.com/ottouk_77/68mustang.htm
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Pierre
Gearhead Posts: 516
From: Near Paris, France
Registered: Apr 2002
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posted 12-11-2003 09:33 AM
This is humble experience on the issue:There was an article in Mustang & Fords on gauges "how to fix them", and among them on tach. In its original set up a tach works as an ammeter and is therefore in serie with the coil's primary circuit (unplug the tach and your engine will stop). It displays the current intensity that goes through the coil. I remember that a resistor was in serie as well.
It goes: +12V-ignition switch-resistor- coil primary-distributor-ground Now; if you are using an optical/magnetical triggering device in the distributor, you are changing the circuit's configuration in terms of impedance and that may affect the precision of the tach, it may not work at all
I would really call up the duraspark people to see what they recommend, they may sell an adapter like MSD does on their 6 serie capacitive discharge box. I can scan the diagram from Mustang and ford and email it to you if it helps but there really isn't much to it !
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Fastback68
Gearhead Posts: 2703
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 12-11-2003 10:51 AM
Ooooo guys, let me run all this by the electrician first, see if we need any diagrams. Pierre's way is the way I've read about it. I recognize the words, I just don't understand it myself. Electrics are like ancient Greek to me.
Phil, one question. It sounds like you've found a way to "make it work", but is your tach an original factory piece, and do you have electronic ignition?
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indyphil
Gearhead Posts: 2047
From: Senoia, G.A. USA
Registered: Jul 2002
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posted 12-11-2003 02:48 PM
No mine is a more modern autogage tach, and it is with an electronic ignition yes. If the coil is being grounded by something (points or a transistorised pertrnoix type system) it still triggers a tach the same. Im not sure about duraspark and MSD systems becuase they use the coil differently.------------------
'68 coupe 289 C code
66 heads, edel 600cfm carb, performer intake, dual exhaust http://www.geocities.com/ottouk_77/68mustang.htm
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Fastback68
Gearhead Posts: 2703
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 12-16-2003 08:39 PM
Well, that ended in abject failure  Actually, I think this is all beyond my electrician. He's still convinced there's no way for the parking lights not to be on permanently while the headlights are on
quote:
I can scan the diagram from Mustang and ford and email it to you if it helps but there really isn't much to it !
Could you please? Any time is OK, next year even. I'd really appreciate it! Phil, thanks for the offer too, but I think I'll start with Pierre's since yours is not a factory tach.
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Pierre
Gearhead Posts: 516
From: Near Paris, France
Registered: Apr 2002
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posted 12-18-2003 04:53 AM
quote:
Originally posted by Fastback68:
Well, that ended in abject failure Actually, I think this is all beyond my electrician. He's still convinced there's no way for the parking lights not to be on permanently while the headlights are on
[QUOTE]I can scan the diagram from Mustang and ford and email it to you if it helps but there really isn't much to it !
Could you please? Any time is OK, next year even. I'd really appreciate it! Phil, thanks for the offer too, but I think I'll start with Pierre's since yours is not a factory tach.[/QUOTE]
Done, via email
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Fastback68
Gearhead Posts: 2703
From: Sucat, Paranaque, Philippines
Registered: Jul 99
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posted 12-18-2003 07:15 PM
"Mercy buckets" as my Mum would say  Pierre, you understand that right? It's good ol' London French!
For future readers of this thread, the info Pierre sent me seems really clear and simple. If I forget to post a report here after I've tried using it, and you have the same problem, drop me an e-mail and I'll forward it.
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