What gauge is wire inside ignition cable?

[REByar]

Hi,
While having other engine work done on my 1928 Tudor the mechanic replaced the ignition cable. I am not sure why but he did. I had either an original ignition cable or an old one with just the wire coming out the terminal box end. When I rewired the car 2 years ago I did not change this just replaced the other wiring (dash and lighting harness). The wire coming from the ignition cable to the ignition switch was heavier-like 12ga. But now the replacement ignition cable wire is much smaller- like a 16ga. I understand the wire I had was cloth covered and the new one is not. But still the wire itself appears to be of thinner gauge. I ask this because since getting the car back from his shop I have had the car stop running after about 15-20 min. The lights and horn all work. But after this period I check for a spark and there is no longer one showing. So I was wanted to know what the gauge should be and if this cable is too small could it be heating up the coil which is shutting down the engine.
Any help would be greatly appreciated.
Thanks
REB