There are no visible aerial wires on the P-38J, nor any other model that I know of. We have an L model in our museum with no visible aerial wires.
I have seen only one photo of a P-40 with an aerial wire. Different radio set than normal? I don't know for sure, but from what I have seen, I don't think the P-40 had visible aerial wires. I am by no means an expert on the P-40, though. Here is the one shot with an aerial wire.