lighting problem



I'm having a problem with the instrument cluster lighting. with the lights off, my tach & boost LED's work fine. With the headlights on, I have no lights at all inside & the LED's go out.
Anybody got any ideas????

first thing I can think of is the dimmer knob--it's just a rheostat, and it may be bad? Also, how's the inst. panel fuse?
the same thing happened to my 84GN i found two plugs behind the grovebox when i put the two back to gather mine did the same thing and took out fuse disconnected the two plug,s and it work,s fine now.
It's a fuse or the dimmer switch. If I remember right the tail light fuse makes it do that.

Thanks for the replies. Unfortunately the car is DOA now. Lost oil pressure, so I haven't gotten to check the electrical out yet. I'll post to let everyone know when I finally get it fixed.