Elec. Tech Help- Gauges

While running with just daytime headlights on, gauges will read normal...

If I turn headlight switch to on, with all running lights on, my fuel gauge, oil pressure, and temp gauge will lock in positon and not move ( can drive 400 miles and fuel gauge will not move, nor oil pressure ect..)

Turn headlight switch to OFF while driving and oil and temp will slowly read where they should be. Turn engine off for 10 min. and restart, fuel gauge will drop to accurate amount, oil pressure will read normal, temp will read normal.
This has been going on for 3 years since I purchased this used 99 burb.
Have replaced ground wire batt. to engine, added extra ground to frame and chassie ground with no change...
WHAT AM I OVERLOOKING ????
Is there a ground problem?
Headlight switch ground??
Would a bad DIODE in the Alt. cause this???
Anyone with a cure ?????
HELP !!

Red: Funny thing I found in my '98 C/K service manual schematics. The gauges fuse not only powers the gauges but also the DRL Relay and the DRL light. The relay also gets a signal from the DRL Module, probably a ground. Could it be one of those causing your problem? Try taking the relay out and see what happens. It's located in the convenience center(lower left firewall, relay is bottom center)............Steve

Thanks Stickman, I'm up to try anything.
Will attemp that tommorow, takes awhile of driving to see if the gauges will operate properly especially the fuel gauge.