Topic: Yellow Top Coil

[markb0729]

I've had my fair share of troubles with after market ignition coils so I've been keeping my eye out for an original Yellow Top Coil that's in very good condition and/or can be cleaned up and be presentable at car shows.  I'll pay more for one that is excellent condition but jeez, prices seem high to me.  Anyway, I came across this coil on eBay and it looks pretty good.  The coil appears to be an original yellow top coil but there is not any signs of an ink stamp.  Seller says that it works but I sent a message asking if they could get me the primary and secondary resistance readings.  What do you think, original?  Seems to be in visually good shape and the price hasn't been bid up...  yet.

Mark


Sellers Description:

FORD YELLOW TOP OR MUSTARD TOP COIL: this is a used coil for the classic Ford or Mercury, it is the yellow top. this came from an estate auction of an old Ford mechanic, it was in his desk drawer. I did have it tested and it has good spark. this coil has no ink stamp to show a part number. you classic Ford folks will have to sort that out to see if it will do the job for you. it has the dist. and bat. markings. I was told this coil was used on the Fords and Mustangs and Mercury Cougars 1965 1966 1967 1968 1969 1970 1971 1972. the buyer will pay 9.80 S&H.

Pictures:

[196667Bob]

A couple of things to be aware of on your yellow top coil. First, they were first used by Ford in 1957. The earlier ones (57 to about 64) had a "bump" on them for indexing on the coil bracket (see attached picture). The later ones, from about 1965 on didn't have this bump.
As far as testing, what I normally do is after testing the primary and secondary resistances, is take my heat gun (or hair dryer if you don't have one), and bring it up to 150 degrees, which is about the operating temperature of a coil in a warmed up engine. If the resistances stay close to the "cold" coil resistances, you should be good. When the coils go bad, they usually break down under heat, and will give erratic readings.
In regard to the coils appearance, besides repainting the semi-gloss black, you can restore the yellow top if needed, using Rustoleum Satin Amber spray paint. It's very, very close to the original mustard top. Just do a careful taping job, and don't forget to tape off the Dist and Bat posts, and the inside of the "tower" where the coil wire goes.
As far as finding an original, you might check Mustangs, Etc. A couple years ago, they had a good supply of used ones that had tested (although not with the heat), at reasonable prices.
Hope this helps.

Bob

[markb0729]

Bob, thanks for the info and advice.  Every little bit helps.  I sent off an email to Mustangs, Etc.  I'll see what they say.

Mark

[196667Bob]

There was a question when I looked at this Post this morning that asked, "How do you test a coil ?". It has apparently, since been removed, but since I have prepared an answer, I will still Post it, since it is a valid question.
Typically, one might see a "Coil Test Procedure" something like I have attached (from the 1957 Ford and T-Bird Shop Manual). It notes what you are testing, and why, as well as testing at normal operating temperature (as I noted previously), but it doesn't tell you how to do it. It really is a rather simple procedure.
First, you need a multimeter (Volt/Ohmmeter) capable of reading 200 ohms, and 200,000 (200K) ohms. Also a heat gun (or hair dryer if you don't have a heat gun), and a way to measure the temperature of the coil (I use an infrared thermometer). An option to the heat gun and thermometer, is to start the car (after the "cold" testing), and bring the engine up to normal operating temperature. Then disconnect all wires from the coil, including the Distributor to Coil wire. Then do the test on the hot coil.
The test procedures are as follows :

1) For Coil Primary Resistance, set the meter to the 200 ohm scale.
2) Connect the Red lead to the "Bat" (+) terminal of the Coil, and the Black lead to the "Dist" (-) terminal.
3) Record your reading (for 1965-67 Mustangs, should ideally be 1.4 to 1.54 ohms.
4) For the Coil Secondary Resistance, set the meter to the 200K scale, leave the Black lead of the meter connected to the "Dist" terminal, and move the Red lead to the Coil tower (where the wire from the Distributor was), making sure that the lead makes contact with the connection at the bottom of the tower. This reading should be somewhere between 7600 and 8800 ohms (although I have seen some used "good coils" as high as 30,000 ohms). Record your results.
5) Repeat the same tests on the Coil at operating temperature and observe if it is a steady reading. Record your results again.
6) Compare the results. If the results of the "hot Coil" vary significantly or are much lower, then the coil is breaking down when hot, and should be replaced. All results are significantly higher or lower, then it should also probably be replaced. The values shown in books are typically for "new" coils, and some differences are to be expected with old or well used coils.

You can now be labeled a "Doctor of Coil Resistology".

Hope this has helped.

Bob

[J_Speegle]

Mark interesting that the one you show in your post lacks the markings between the post. Haven't really studied when that started or if it relates to the type of coil, date or other detail we have yet to discover but thought I would mention it. There are multiple applications and there are some that are slightly smaller than what was factory for our Mustangs. Bleive they were shorter by just a little

[Brian Conway]

Thanks Bob.  I posted the ' how to ' question and then pulled it.  Electrical issues and tests are a challenge for me.  For example; I tested a couple of coils and got 2.2 for the first test and 1.0 for the second test.  Of course nothing agrees with the ' test procedure '.  Brian

[jwc66k]

Also a heat gun (or hair dryer if you don't have a heat gun), and a way to measure the temperature of the coil (I use an infrared thermometer).

Or you could put the coil in the oven set to 150F for 15-20 minutes. Use a "hot" glove to handle.
Jim

[J_Speegle]

Do have some verbage related to the testing of the primary and secondary windings of the coil in preparation for an article on restoring coils. Will see if I can locate that and post

[preaction]

Mark, I have an extra can of the spray paint used to reproduce the yellow color of the coil email if you need one as Im not far away.

[markb0729]

Great info guys, much appreciated!

preaction, I'll take you up on your offer for the yellow paint.  I'll send you an email. 

Mark

[196667Bob]

Brian : A couple of things on your "Testing Procedure". First, a variance between readings of 1.0 and 2.2 is not common. Do you have the meter set on the lowest scale that would cover the typical Primary Resistance ? This is typically "200", but you may want to go up one scale, take a reading, then go back to the lowest scale. Are the batteries in the meter good ? Unlike Volt and Amp readings, Resistance readings rely on voltage from the batteries in order to measure ohms. Have you checked the accuracy of the meter ? This can be done by measuring the resistance of a known item; this would be like a resistor of known value.
Finally, values that I noted are printed values which are generally based on new, or like new coils.
That being said, I have read from many sources that "in general", values of Primary Resistance should be between 1.0 and 2.0 ohms; values for Secondary Resistance should "generally" be between 7500 and 9000 ohms (this value does vary between automobile manufacturers). Any readings beyond these "general" guidelines, would normally dictate that the coil be replaced.
One other thing to remember is that the Test Equipment that was used to come up with the printed values can vary, to some extent, from that being used on a current test.

Just a few things to think about before getting rid of that "bad coil".  One other item to consider; how does it perform when installed ?

Bob

[preaction]

This topic is uncovering many things, as I took a closer look at two spare coils to test testing them I found that both have info between the terminals one has 8A and the other has 7D would these be date codes ?

[Bob Gaines]

This topic is uncovering many things, as I took a closer look at two spare coils to test testing them I found that both have info between the terminals one has 8A and the other has 7D would these be date codes ?

those are not date codes. Date codes are on the ink stamp. Maybe a batch code for the mfg. it is one thing missing from the repros.

[196667Bob]

Maybe a batch code for the mfg. it is one thing missing from the repros.

Bob : I wouldn't go so far as to say that these markings are "missing" from the Repros. While Mannel also notes in his book that these are not "date codes", he also notes that the meaning of these markings is "unknown". As I noted previously, these "yellow top" coils were used from 1957 (January), through the 70's, and available as Service Parts for many years after. I have these "yellow top" coils for my 57 Retractable and T-Bird, my 59 Retractable and Ranchero, my 62 T-Bird, my 66 Mustang and T-Bird, and my 67 Mustang, as well as a few spares. The majority of the ones I have exhibit no markings between the posts. While, unfortunately, I can't say which, if any, are original assembly line coils, I would find it unusual if the majority were not. I say this due to the fact that it is fairly uncommon for a coil to really "go bad", and thus that so many of mine have no markings there - of course it is a possibility. Maybe the ones with the markings were "assembly line only", and the ones without were Service Parts ? Or possibly just from different suppliers for the Plants ? In any case, I think it is something that requires further investigation/documentation before saying that all yellow top coils should have the marking between the posts.

Actually, I am more interested in something else that occurred with these "yellow top" coils. When the first 12 volt coil was first used in 1956, it was Part # B6A-12029-B, and was black, with a black top. In January of 1957, the coil received the "yellow top". In early 1965, the indexing "bump" on the coil was eliminated. In 1967, the coil became stamped "Autolite". Then, and I don't know what year for sure, the "yellow top" was eliminated, and, at least the Service Part, became black again. The Service Part remained like this until it was "Not Replaced" sometime after 1990 (again, I don't know when since my last OSI catalog is 1990), but do know that it is no longer available 'due to low demand". Throughout all of these changes, the Part # remained B6A-12029-B. The "something else" that I am curious about occurred sometime during the "yellow top" era ; the tower of the coil (where the wire from the distributor plugs in), became longer. When did this occur, and why ? Possibly a supplier variation ? Once again, not enough of a variation to warrant Ford changing Part Numbers", or even a suffix. As I have come across some of these, I am interested in finding out the details.

Bob

 

[J_Speegle]

................In 1967, the coil became stamped "Autolite".

That change took place in 1966 as discussed in a tread a couple of days ago

Check this thread out -  https://www.concoursmustang.com/forum/index.php?topic=2947.new#new

For the period of cars we consider the classic years of Mustangs al of the originals I can recall had the small letter and number cast in the yellow portion of the coil