radio went black after using car charger

Check the fuses, especially the memory fuse. That is tied in with some other circuit, typically the interior lights, horn, or cigarette lighter.

Do you know if there is a fuse on the back of the radio?

Also,do you have a diagram for the cigarette lighter?

My diagram doesn't show a fuse on the back of the radio. The interior lights fuse feeds the radio's memory circuit. If that circuit is dead, the clock will reset to 10:00 or 12:00 each time you turn the ignition switch on.

Also consider that a lot of GM radios from this time period used a small light bulb to back-light the LCD display. Some use three bulbs. If this is the type of display you have, you should be able to see the outline of the digits if you look real close.

GM is very proud of their display bulbs. Some dealers will tell you the only way to get a replacement is to send the radio in to one of their two grossly-over-priced repair centers. Some dealers will sell you a new bulb in its socket, but will charge as much as $24.00 for it. I use "grain-of-wheat" bulbs, and solder the leads to the circuit board where the socket twisted in. You can find those at Radio Shack and any online electronics parts stores for less than a buck. If you do that, be sure the bulb is turned so the filament is facing the display. That just insures the display is lit evenly from side to side.