head for two areas:

First, the fuse panel. Give every fuse a twist. Use a forefinger and "rock" the fuse in its holder. That removes oxide build-up, and may reveal a fuse that is blown but doesn't look it.

Second, check the ground connection on the head and tail lights. When they get oxidized, voltage can back-feed into other areas, giving odd results.

The bulb failure warning relay (BFWR) can fail, but it's a lot more difficult that the first two approaches, and more expensive to replace.

Let's see if I uderstand your symptoms: Night time, turn on the headlights. (Is the engine running or not?) You say "my dash lights including the instrument cluster won't go on." There are lights that illuminate the gauges and speedo and clock/tach, there are warning lights along the bottom edge of the instrument cluster, there are lights that illuminate the things on the control panel. Which of these do or do not come on?

There is a relay that switches the high beam / low beam, otherwise there are no relays in the headlight/marker light system.

If you suspect the BFWR, there are two types used in the 240-740 series. Cars without a high-level brake light have a relay different from those with the light. You need one from 1985 and older, any year will do. Get a few from a boneyard.

Good Luck,

Bob

:>)