I'm new to the group and have a question that's undoubtedly been asked
thousands of times before.

My car is in excellent condition with relatively low mileage (60K) and is
driven infrequently (one weekend per month).  Just recently I've experienced
an annoying problem that I believe is electrical and I'd appreciate ideas on
where to start troubleshooting.

The instruments have become increasingly "jumpy"  and erratic while driving.
The tachometer swings fairly wildly from 2500 to 3500 at highway speeds
while the engine is clearly running the same speed.  In addition, some
instruments are affected by tunring on the lights.  I see a perceptible drop
in the oil pressure and fuel level readings when the light switch is
activated.

Ideas?

Thanks.