I have come across several coils. One I know is a 12 volt. The other two are not marked. All are Delco-Remy.

1) How can I determine the difference between a 12V and 6V coil?

2) How are these tested to determine operability?

Thanks, 37Blue

Usually an old 6 volt will have no volt number on it....like if its from before the 12 V years.

If we discuss in technical language then it can be said that 12v coil contains higher internal resistance to limit the total current as compared to 6V coil.

Found testing info on the Jim Carter truck parts website.

Try this link.

http://www.oldchevytrucks.com/blog/index.php/2010/02/coil-testing/

The site also lists some interesting solutions to car maintenance problems back "in the day".

Why is the condenser needed to run this test? Thanks, Mike

A condenser with case grounded is necessary to achieve a strong spark. Without a condenser the spark will be weak.

6V coils usually measure 1,5 ohms primary resistance, 12V coils 3 ohms or thereabouts.Picture shows 2 coils in parallel and the condenser is there in case the tested coil linkup includes an open condenser in the distributor. 2 condensers in parallel would not stop car from starting.Shorted condenser would. See Ed Packers book "Electric Trouble Shooting on the Motor Car"

This question of Is the coil Bad? Or the high tension coil wire bad? Or is it the condenser? or is it the breaker points?
Coils are hard to test with a multimeter on the bench, the ohms readings don't consider the loading and the huge changes in voltage flux, it is easier to change them out with a new one or one that you have tested on a good running engine.
I do use a ohmmeter with a very high resistance scale to test a condenser for a good capacitance kick. Or you can charge a condenser up on a spark plug terminal and lay it on a wooden workbench with the lead wire hanging over the side of the workbench and let your buddie pick it up and test it for you. ZZZAAAAPPPP! Ha!
This test setup on the Carter site is ridiculus!, you can have the condenser changed out, engine test run,then the coil changed out engine test run, and the points visually checked and the gap measured while getting all the wire, tape and clips you need, then you would be getting the tape job done and the wireing figured out, then whether the test shows the coil to be good or bad, you have to disassemble the octopus looking apparatus! Do it right and do it once.
Get a life!