Clean 12v switched source that is hot cranking and running

DionR said
My ‘74 has a circuit in the fuse box that powers the instrument panel, fuse #6. It comes off the blue IGN1 wire and is only powered in run. It’s the only one that does that though.

Did the earlier cars not go through the fuse box to power the IP?

But that is part of the problem. That line basically is the same as IGN1 so it goes dead in crank