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Old 09-26-2009, 02:32 PM
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Daily Driver 67 Mustang Electrical system issue - At the end of my rope -

Hopefully someone out there can help...

At idle the tach shows the 600 - 750 rpm it should... for about 5 minutes, then the needle starts bouncing around 3000 - 4000. If I turn on all the accessories it may calm back down, but may not either. At 70mph / 2300 rpm it also seem to even out.

I have a 1967 Mustang with a 351W out of a 69.
I replaced the points distributor with a Accel breakerless (71204e) about 4 years ago. I am running a matching Accel Coil. Accel 10.8mm wires. 100 amp single wire alternator.

First the module in the distributor burned out. I replaced that, but noticed that the coil was getting extremely hot. That is when I first noticed the Tach Issue.

As the coil has never run that hot before, I figured that maybe the coil had caused the module to burn, so I replaced the coil with another matching Accel coil. This did nothing to alleviate the tach issue. I tested the setup with a new AutoMeter tach - the new tach does exactly as the old did.

I have a new Painless wiring harness throughout, but checked the wiring anyway. I ran a new ground wire from the distributor to the Block eliminating connectors and shortening the length and increasing the size of the wire, as the one on it looked like it got a bit hot at one time.

I checked all grounds from block to body (I have 2 something like 2 gauge grounding cables).

I checked the ground to the tach and switched it to another ground just to make sure, but this made no difference.

I pulled the alternator and had it bench tested under load for about 10 minutes, but the alternator shop swears that the alternator has no issues.

So now I am at a loss - I mean that is really all there is on a 67: Alternator, coil, distributor/module.. and of course the Tach strung together with some high dollar wire...

Any help would be appreciated...

Thank You

Lee

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Old 09-26-2009, 03:05 PM
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Couple questions

Does the new coil run cooler.
Where exactly is the tach wire connected and is it where the ignition manufacturer suggests.

It sounds like you have a ground that is failing for some reason after it runs for a while. Does the tach light work. Have you checked the feed voltage for the tach bot when it is good and when it goes crazy.
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Old 09-26-2009, 09:18 PM
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The new coil does run cooler, but the old coil was a cannister type and the new one is a e-coil (both of similar eletrical spec & both Accel matched to the Accel breakerless distributor), so I'm not sure what it's normal temo is.

Tach wire is connected per specification to the "-" side of the coil.

Tach light does work.

I have run the tach on two different grounds - both I am sure of and test as good grounds.

Voltage at the Tach in the few minutes its running right is between 8 -10 V. When the tach is not running right the Voltage is between 12 - 14 V.

I think the difference in voltage is that it takes the one wire alternator a few minutes at idle to start charging to full levels.

But the Tach was running with the same setup just fine for a couple or years or more prior to the module burning out .

Now leading up to the module going out the car would run on the highway and in town for about an hour then begin to just die (like turning off the key). When this happened even at speed you could not roll start it (manual 5spd trans). You had to shut the key off and turn it back on, then it would start right up. Once it died the first time you could figure on it doing it every 5 - 20 minutes until you parked.

Finally the module smoked. When it was replaced I had the very hot coil issue, and the tach issue..

Operating temp during the shutdown issue was only 180 - 190 F.

Thank You

Lee
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Old 09-26-2009, 09:38 PM
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what type of tach

If I remember right ford used input from the alternator for a few years on some cars instead of the dist and that did not give acurate readings, Is it factory or aftermarket tach.
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Old 09-27-2009, 10:46 AM
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It is an aftermarket tach, fed from the negative post of the coil - but has been running in this car with setup for 4 years...
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Old 09-27-2009, 11:29 AM
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Ok basic of basics, you need to get the voltage up to spec at idle first, low voltage cause higher current and will burn up anything electronic.. Until you get this fixed you are wasting your time. If it were me I would lose the 1 wire, get a 3 wire. This will solve your voltage issues and will make an overall great improvement to your electrical systems health.
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Old 09-27-2009, 02:06 PM
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I agree, get rid of the 1 wire alternator and get a good 3 wire.

Vince
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