I bought a 6 volt input, 45,000 volt output coil for the T. I've had it in service for maybe 150 miles. Today while running the T in the shop after installing new plugs, the engine shut off like I had turned the ignition key off. It had been running pretty good after putting the plugs in and just cut off after about 8 minutes of running . After three hours of troubleshooting, I changed the condenser, cleaned and re gaped the points and got fire at the plugs again but it is running rough. I have good battery voltage (6.44 volts while running). Do the high performance coils require a special condenser? I am running a Texas T distributor and was using the condenser that came with it. I'm not sure what the condenser is for that I have on it now, it was one I had laying around the shop and put it on there just to try it. I have ordered a new points, coil and condenser from Langs to put back on it. I would like to run the high performance coil but need it to be reliable.
The coil might need a ballast resistor before the coil. Was there any instructions with the coil that said this? I know it is common for a lot of 12v systems (like muscle car stuff) to use a ballast resistor to reduce the input voltage so it doesn't burn out other parts of the ignition system.
I wonder who is the manufacture of the coil--an ID on it?
I think the condenser needs to be matched to the coil.
They are (supposed to be) a set as Les mentioned but many seem to work OK with different coils. You can re-install the old condenser to see if that was actually the problem and not the coil overheating/failing. It is unusual to see a condenser fail.
If the coil needed a resistor it would have burned the points out.
A condenser is a condenser.
I'm betting you have a crappy coil. Probably made in Mexico.
Go to NAPA and get a coil for a '66 VW (6 volt). don't use a resistor, the coil has one built in.
First check for loose low tension wires, at the connections.
Also, a coil only puts out enough electricity to jump any gaps between it and the center electrode in the spark plug.
With a plug gap of .020 to .030" and a compression ratio of less than 4 to one, or even 7 to 1 the coil will never need to put out more than 12,000 volts.
My point is: no need to by a hot coil for a model T. It won't help or make any difference.
Ballast resistor reduces current.
Aaron is exactly correct. Another source for 6 volt coils is Tractor Supply. Ford ran 6 volt on farm tractors through 1964.