Well, thanks for the suggestions and to this forum. I found and fixed the problem!!!
First off, I located the service manual for my car on this site which was invaluable for understanding the workings of the DRL
This, along with the comment above, helped me zero in on the likely culprit - the "Daytime Light Control Unit" (and to find it in the engine compartment).
A couple of taps on the unit caused the headlights to flicker, so that's got to be a good sign that the problem is there.
A call to the local stealer - $270 for a replacement. Ouch. A call to the local auto wreckers - no G35's. So back to the internet and search for Daytime Light Control Unit and there are a whole load of posts on the Nissan forums about the unit and cracked solder connections, and that it is not too difficult to find and repair. So I did ....
Here are a series of photos that show the steps. The research took 4 days, the repair took about 30 minutes.
Here is the location of the unit in the engine compartment
A little closer after removing it (easy)
Now for the fun part - open it up. There are 4 small plastic tabs that can be moved with a small screw driver,
Here are the insides - pretty simple for $270!!!
And the backside with all the soldering. See the suspicious area?
And zooming in .... Yup, that is a cracked solder connection. I applied some more solder with a soldering iron, and it's good as new. Reassembled everything and put it back in the car. Yes!!!