Hi all,

I'm playing with a transformer coil, and I can't determine what wire corresponds to what.

There's a black, red, and yellow. The red and yellow have blade connectors. The black is shorter and has a ring connector. There is 0 resistance between the red/yellow, and +40megOhms between the red/black and yellow/black.

My deduction is that the black is the positive of the secondary winding. Red is probably primary positive, yellow primary negative. The secondary probably needs an isolated ground, or could possibly be tied back into the primary negative. I think this was an auto coil....
Thanks

 

From your description, there is only a single coil.

The coil red/yellow is probably a secondary coil because it has near zero resistance. Black is a screen connection so it is fitted with a ring terminal for connection to the chassis or ground.

 

What do you mean by screen connection?

Also, I have to assume this is dual coils, since the other auto coil I have is 3 wires as well... Maybe I'm misinterpreting the definition of an auto ignition coil?

 

A screen is a metallic layer between windings but insulated from both windings.

Without this screen, there will be capacitance between two windings and surge and spikes can easily coupled from one winding onto the other.

If this screen is connected to ground, then inter windings capacitance disappeared as they now only have capacitance to ground instead.