90 Beretta lighting prob - what have I done?

1990 Beretta GT - 3.1, Digital Dash. Current symptom: DRLs work normally, but the automatic headlights don't come on. If you turn the headlights on manually, the digital dash goes out. Unless you turn the dimmer control all the way on - in which case the dome light doesn't come on and the dash lights come on.

I also found a blown fuse - I can't rememeber which one - the car's not at work with me...might have been the DRL fuse or the dash light fuse.

I suspect I may have blown the dimmer "module" - where is it located? For some reason the Helms manual is totally vague on this and tracing the wires is a PITA without a total dash disassembly.

The car has an aftermarket radio which hasn't ever caused problems - it's "plugged into" the factory harness with a kit. However, I did have it and the HVAC controls out this summer - coinciding with this problem happening. I think I shorted something out - am looking for suggestions on where to start - everything looks ok - no smoke.

Argh. Nothing like fixing one thing and blowing up two more things.

Ray