[Jim in Wisconsin]

The ignition resistors on the early v8s seem to be sort of a mystery, at least to me. A lot of times the original ones are rusty and bad looking, but I've heard the modern replacements are not very good.
The Mac catalog says their's is 40 ohm, which seems completly wrong to me. Any old ones I find measure very little resistance, like maybe a half ohm or so. I heard that they were supposed to increase resistance when they heated up, which would make some sense - for easier starting. I've tried heating them with a heat gun- got them too hot to touch and don't see any change in the reading.
I know they are needed, because I've seen coils melt when they weren't in the circuit. The primary resistance of the coil is only a few ohms, so the resistor would only need to be a small amount to change the current. How can we tell a good one from a bad one? How much current can a coil handle without melting? Any thoughts?
Jim S.