Dash lights go off when head lights go on?
Check the fuse box for the headlight switch. Possibly a relay
problem or a burnt connection. Easy to replace - part available at
most auto stores (NAPA, Auto Parts, etc.), depending on the make
and model of your vehicle. check the contacts inside your
headlight,interior and dash light switch (that is all one) and put
some electrical gease in there so it make a good contact.