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Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 07-04-2012   #1 (permalink)
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Default Radio Noise Suppressing Capacitor

Hello everyone! I have a 1967 mustang and I was wondering if not having a noise suppressing capacitor effects the ignition system in any harmful way. I do not have a radio currently so radio noise isn't a concern right now. But iv'e recently read that lack of a suppressing cap can cause coil to not produce a spark. After reviewing a schematic, it doesn't seem like the cap can effect the coil, but i want to make sure. I've attached the schematic below. The capacitor should be connected to wire 152A, which is connected to the voltage regulator connector. The fact that wire 152A has a * instead of the cap means that the wire function is not applicable to the circuit, but this diagram is of the ignition system so if the cap isn't applicable to the ignition system I'm thinking it doesn't effect the coil. Any ideas would be helpful.

Thanks,
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Unread 07-04-2012   #2 (permalink)
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The only supressors on the Mustang were on (or in) the alternator, and on the voltage regulator. These, or lack of them, would have no effect on operation of the ignition system.
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Unread 07-04-2012   #3 (permalink)
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ok thanks for the info, I attached a pic of the regulator and the capacitor.
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Unread 07-04-2012   #4 (permalink)
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Your reading material must have been in the fiction section?

The suppression capacitors were nearly universal in the latter days of generators. Commutator noise from the generator would cause loud static in an AM radio. With alternators there is no commutator and its not much of a problem. The reception in either of the original radios in my 66's is the same with, or without the suppression cap. Today you can't even buy a new one since no one has used one on a car in decades. To fake it for a semblance of originality you can use an ignition capacitor, i.e. condenser, which looks like what might be used in your picture.

Unless used in the distributor they never had anything to do with how the ignition worked.
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Unread 07-04-2012   #5 (permalink)
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Like mentioned it's not needed anymore. The original one that was on my 68 had the wire fall out of it (broken) and I had none on there for awhile. I wanted one just to complete the engine compartment and discovered they are on Ebay often, I was able to get several of them. They were used on most Ford, Mercury and Lincoln products at that time.
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Thanks for all the info guys. By the way I read that on Autozone's website under the product description for a radio capacitor. Maybe they're confusing it with an ignition condenser!
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Unread 07-05-2012   #7 (permalink)
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Radio suppression capacitors were used in several places, voltage regulator (due to the contacts opening and closing), the + contact on the coil (primary voltage goes to 250 volts when the points open), alternator (produces a triple sinewave of dc current of varying frequency), etc. The biggest noise suppressor is the battery, the closer it is to the electrical the better. If you had a oscilloscope, you could see all of these variations on the dc in the car, it is also different at various locations in the car, it is always more pronounced at the source of the electrical noise. Dc generators do generate more electrical noise than an alternator, but a alternator does produce a whine, that is heard in some radios, this is removed or weakened by installing a choke (inductor) and a large electrolytic capacitor in line with the power to the radio. The suppression cap on the coil, has little or no effect on the spark to the spark plug. Good Luck.
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Unread 07-05-2012   #8 (permalink)
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John,

Interesting trivia I had not seen previously.

If you search AutoZone for 'radio capacitor' it says there are no parts by that name. However, you also get a 'Points and condenser' link which brings you to two 'radio capacitors' which AZ sells (while saying they don't??). Both are made by Wells Vehicle Electronics which I also never heard of. Seems they built the Norden Bomb Sights in WWII; that business has been slack for a few decades.

Going to Wells website its also hard to find these but under 'Specialty Applications/Capacitors' you get 4 choices which are all 'radio capacitors' which I didn't know anyone still made. Two of them are sold by AZ but this verifies that the AZ listed lead lengths in FEET should really read 'inches'. Only the URS1500 has any electrical data listed: 0.5 MFD, shorthand for 0.5 microfarad. The app note says: Universal type for noise elimination for generator brush arcing. The original Ford caps were also ~0.5 microfarads so that isn't electrically far from an original. Their own words though hint that its not much good on a alternator whose 'noise' is more a single frequency sine wave whine that a single capacitor won't help much.

Knowing that a regular ignition condenser is the same item except with half the capacitance (~0.25 microfard) the $15.99 is also kinda pricey especially without the Ford bullet connector on the end.

The technical description at AZ is pure techo-babble written by someone who hasn't a clue what these are or do. They have little to do with the (ignition) coil current; the noise generated from the coil is mostly RF noise that goes through the air and is unaffected by a radio condenser on the 12V power. You put resistors in the spark plug wires for that kind of noise. Some cars did have caps at the coil for noise suppression on the input power but Ford never put one there on a Mustang. And to suggest that not replacing this part will somehow cause "no spark and/or no-start" is pure and simple fantasy.

Seems these have been around awhile. This one looks fairly 'vintage': http://www.ebay.com/itm/Wells-URS1500-Condenser-/110808885114


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