I have a 2004 Bonneville GXP and for the past 8 months, the HUD has worked when it'* felt like it. My blower fan has also acted the same way, but not near as frequently. I realize they are on the same circuit, but can't seem to figure out the problem. Have checked the fuses and the connection at the blower motor with no luck. Have been unable to find where they are both grounded on the firewall. I am ready to take the entire dash off if need be, just don't want to have to go to the dealer. Any suggestions are much appreciated!!

has the car sat for any length of time without being used? if so mice or something may have gotten in there some how and knawed the wires

It looks like blower motor an hud have separate fuses, but they do share a common ground Passenger Compartment, Lower Left Front Corner splices in to right side body harness. Maybe the 2 issues aren't related Maybe HUD problem is HUD dimmer. and fan is just the fan with a lazy gerbil.
These cars have become computers on wheels everything that operates inside the cabin is reliant on data not plain old electricity.

I've had my blower motor not work once; on a single digit cold morning. The car would warm up but the blower wouldn't spin, so I pulled over, popped the hood open, pulled out the cabin filter, and gave the blower a spin and off it went. Worked fine since then.

I can't say I've had any issues with the HUD though, aside from my impression that it should be brighter.

I appreciate the ideas given! Got the dash off Wednesday and found no evidence of any rodent problem or burnt wires...the HUD has worked with no problem since the dash removal, but I've left it off for now just to wait and see. The blower connection seemed a little loose, so I used some long zip ties to tighten the connection and so far so good. I guess now we wait...I'm sure that once I put it all back together it'll start acting up again

HUDs are also known to have a problem with one of the solder joints
maybe that could be the reason and once removed it hooked back on.. JMO