Is my coil bad?

beast_3

beast_3

Member
I've been trying to get my '30 Tudor back on the road after a 2 yr. hiatus & I think I have a bad coil. I'm not getting any spark between the points or from the coil.

I've tested the coil (an old oil filled, repo script coil) with my multi-meter & on the 20 ohm scale I get these readings:

between the + & - terminals scale reads a 0 ohm short
between + or - to center reads 7.9-8 ohms
between + or - to case shows open circuit.

One of my manuals says the short between + & - terminals indicates a bad coil.
Also coil gets hot after leaving ignition switch on while trouble shooting.

I've check & adjusted all the other parts of the ignition & it all checks out OK.

Think my coil is bad or have another problem?
Thanks!
Bob
 
Try another condenser.
If that does not work get another coil from a local auto parts store or from one of the A parts vendors.
 
Coil case should be isolated, so that's fine.
A 6 volt coil should have about 1 1/2 ohms between the primary terminals, and this is hard to measure on many cheap meters.
Ground the red wire on the coil primary terminal and see if your ammeter reads about 4 amps.
 
2X on what Tom said.

Try his suggestion on the ammeter.

Also, if the coil is getting warm when the ignition is turned on then there is likely proper resistance and not a dead short. If it was a dead short, then it would more likey blow a fuse if your car is equipped with a fuse.

Some other things to check:

Capacitor might be shorted. Take it out and put the ohm meter on it. If it shows completely open on an ohm meter or causes the needle to jump, then the cap is likely good, If it shows any low value of resistance, then it is probably toast, and would keep spark from happening.

You should also make sure that the armored cable coming from the ignition swich is not turned in too tightly. If it is too tight, it bottoms out witha short and literally bypasses the points and would cause the kind of problem you are having.
 
Your statement that the coil gets hot leads me to think the points are closed when you're doing the tests and that the coil is probably fine. It doesn't sounds like your case is shorted.

Turn on key with points open, should have battery [6v] voltage at open point arm. If not the cable may well be screwed in too far or some other problem somewhere in the primary circuit.

If you remove the secondary lead and place it near a good ground, open and close points with key on there should be a good spark. [ I don't know how you made the checks].

The info about checking the coil is of course good info.
 
Were the ohm readings taken with the coil connected to the vehicle? This may alter the results and advice.
 
One day I was working on my car and when I installed the instrument panel I just happened to feel the coil getting warm, even though the key was off. The repro switch terminal was rubbing the gas tank and shorting to ground. I had to bend the switch terminals to the side.
 
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