GT40 Sports Ignition Coils.
The GT40 coil comes in two variations.
Firstly, there is the GT40 which is a non-resisted coil to be used in electronic ignition systems.
The second option is the GT40R which is used with a ballast resister, hence the R designation for Resisted usage.
If your car has a white block with a couple of wires coming out of it, usually mounted to the coil bracket or near to the coil, then you need to run a GT40R as a replacement.
You can also buy brand new ballast resistors too, which doesnt hurt to replcae your old one when reconditioning your ignition system.
I know its a simple thing to write, but to get the details down here in one post helps everyone in the end, especially the new members.