I own a 1988 560 Sel none of the dash panel instrument lights work, radio works, roof light works, speedometer and tachometer work but no lights

More then likely it's the stepper mortors inside the instrument cluster . If it were a ground issue more then just speedometer an tach wouldn't be working . Like instrument lighting an rest of gauges . GM had bad stepper motors inside instrument clusters , 2003 to 2006 . Watch this video
https://www.youtube.com/watch?v=oTm2oDx-_GM&t=30s

Hi, this is a pretty common problem on these Silverado instrument clusters. We can definitely help you out with that. Click here to learn more about these Silverado instrument cluster problems: Dr Speedometer Instrument Cluster Repair Speedometer Repair Guage...

When numerous items such as those you mentioned malfunction at the same time, either the instrument cluster relay needs to be replaced or the the instrument cluster connector has come loose.

The instrument panel (refered to as the "IP") is the panel of guages and warning lights that contains the speedometer and tachometer and gauges (if so equipped), it is located in front of the driver and is mounted into the dash.

first check that the dash light dimmer knob is not turned to very dim (far left). It is located in the dash instrument cluster slightly left of center between the tachometer and speedometer near the bottom edge.

If that seems okay, check out the No. 13 fuse in the passenger's side under dash fuse box.

If the fuse is okay, you may have problem with the driver's multiplex control unit. This unit controls lighting for multiple other lights and switch indicating lights.

1. do the park lamps work?
2. dash lamp fuse burnt?
3. is the instrument cluster analog or digital?
4. digital clusters have been known to fail however the cluster lighting is controlled by a body computer.
5. proper diagnosis with require a scan tool that will access the body module ( computer)

sounds like an open to the lights in the instrument panel, if the lights work in the radio, ac panel, etc.

Or, all the bulbs burnt out at once (unlikely).

Maybe the harness to the instrument panel is loose, but only is accessible after removing the dash board.

Take a look at your dome like switch to see if it can dim the overhead light any.If it can't, I would start there. If that checks out, then check all connecters going to the instrument panel to see if any of them are loose.

Chk. fuse, taillights and dash lights should be on same fuse.