I have a Shimano 3N72 dynamo hub wired to an B&M IQ Cyo headlight and a toplight line tail light. Last night as I was riding I noticed that the headlight seemed to alternate between normal riding light and the standlight. The weather was clear and about 70 degrees. The problem did not seem to occur on perfecly smooth pavement. Do I have a fauly connection between the hub and the light? Any opinions/ experience with this problem? Thank you in advance.

I have the same combination of head light, tail light and hub. I have not had this problem. However, I agree with your suspicion that you probably have a faulty connection between the head light and hub. Unless you see signs of damage along with wires, I'd start by redoing the connection to the plastic plug which connects to the hub.

Check for corrosion too.

I was going to do exactly that tonight and check for corrosion too. I have been riding the bike for several weeks recently with another wheel and the little connector piece hanging loose. Maybe the copper wires inside the connector have become fouled or something. I hope it is a simple fix because I really love this lighting setup.