Posted by jdemaris on January 11, 2015 at 11:33:48 from (70.194.15.108):
In Reply to: OT Ballast Risister posted by BSpauld on January 11, 2015 at 11:07:03:
GM converted to 12-volt in 1955. The coils were 12-volt and externally resisted. The same coil was used from 1955 right up until 1975
Generally speaking, coils come in four basic types, 6-volt or 12-volt and either internally resisted or externally resisted. Any coils that do not have an external resistor have one built into the coil itself. That is about all you have to know in order to find a coil that will work in a vehicle with a point distributor. Ford products had their own series of coil designs that did not interchange with any other vehicles from 1928-'48. Ford then began using a conventional 6-volt, externally resisted unit from 1949-'55 and then converted to a 12-volt, externally resisted unit from 1956 to '74. Initially, the resistance unit was mounted to the coil bracket or firewall; however, Ford later went to a pink resistance wire covered with a tar and cloth loom that connected between the ignition switch and the primary side of the coil. Ford changed over to electronic ignition in 1975, so a new "blue top" coil was produced. This coil did not require a resistor and was used until 1990 when the firewall-mounted control modules disappeared and Ford started using thick-film ignition modules mounted directly to the distributor.
General Motors vehicles used the same 6-volt non-resistor ignition coil from 1923-'54. When they converted to 12-volt in 1955, the coils were 12-volt and externally resisted. The same coil was used from 1955 right up until 1975; however, a resistance unit was required on GM vehicles newer than 1963. General Motors changed to their "coil in the cap" electronic ignition in 1975. Chrysler products used the same firewall-mounted coil from 1935-'42, but differences in the ignition switch and cable that attached to them changed every two years or so. You could interchange the coils if your cable and switch assembly could be reused. Mopar changed to the standard 6-volt coil mounted to the manifold when they began automotive production again after WWII in 1946. These 6-volt units did not require an external resistor. The same coil was used from 1946 up to 1955. When Chrysler converted to 12-volt in 1956, they used an externally resisted coil, which was used right up until 1978, even in the electronic ignition-equipped vehicles. Point distributors required a two-terminal resistor with 1.2 ohms of resistance, whereas electronic ignition distributors used a four-terminal resistor with the 1.2 ohms primary and a secondary circuit of .5 ohms resistance. A "tan top" electronic ignition coil was used from 1979-'94, but it used the same four-terminal resistor and will also retrofit any 1956-'78 application. American Motors borrowed several different ignition systems from various sources, and the AMC coils were the same units as the donor ignitions used. From 1951-'55, the Chrysler 6-volt internally resisted unit was used; 1956-'59 cars used the GM externally resisted 12-volt coil. The 1960-'62 V-8 models used a Prestolite Distributor with a Chrysler externally resisted coil (and resistor), but the six-cylinder engines used two different systems: a GM externally resisted unit (the same coil and resistor used on 1955-'63 GM cars) on the Delco distributors and a Chrysler internally resisted coil on six-cylinder cars with a Prestolite distributor. By 1963, AMC had settled on Delco parts for their American-built cars and Prestolite for their Canadian-built vehicles. They continued to use the GM ignition coil with external resistor until 1974. They then tried the Prestolite and Holley electronic ignition system used on International Harvester trucks for a few years. From 1975-'77, Jeep, International and AMC used the same photoelectric sensor-based ignition system but still used the same Delco-style externally resisted coil. They later abandoned the Prestolite system in favor of a Ford electronic ignition setup. This system used a Ford "blue top" electronic ignition coil which did not require an outside resistance unit. In conclusion, there were only about 10 different ignition coils that covered about 90% of the American-built vehicles on the road from the 1930s to the 1980s:
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Today's Featured Article - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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