Had the same problem of a dim headlight on my '72. After trial and error I tracked it down to the fuse / fuse box. I ended up replacing the entire fuse box since getting a good contact was hard. The replacement was fairly easy once the center console was out. The fuse box is (or at least was several years ago) pretty cheap. Mark
I agree with BambiKiller240. It is very easy to replace, albeit a bit messy with the possiblity of radiator fluid leaking into the footwell. You might want to drain your radiator first or at least open it to relieve any pressure. Remove the carpet and padding so as not to leak on them, although chances are, if your asking, they are already wet with fluid. I'm not sure of the official part name but I recall it being called a "valve ****" when I replaced mine. It is, or at least was, an inexpensive part.