Factory Radio stays on after keys are removed, doesn't turn off

1996 GMC Suburban that has over 200k miles.

The only work done recently was having the transmission replaced, no electrical work.

The scenario: My coworker had his transmission replaced over 3 weeks ago with no issues persisting and no electrical issues. It rained heavily last night and he drove home with no issues. He turned off the car and the radio had no power when the keys were removed. This morning about 8 hours later he went to get in his car and the radio was on! This has never happened to him. The car started fine and the battery meter read 15 amps which is perfect charge.

We looked at the fuses to see if that was an issue, no one has tried to break in to the car, the wiring looks good no wear and tear that was noticeable.

One thing was interesting and we can’t get it to repeat now, when he turned on his hazards with the key out of the ignition the radio display was flashing opposite the clicking of the hazard lights. His hazards are blinking correctly (not the fast blinking you get with a bad timer) And one time he turned on the lights and the display flashed once.

So this seems to be a wiring issue, either a short in the ignition or power. This is a 100% pure factory radio with no after market add ons.

Any ideas?

your switch in streeling wheel is bad. move it back and forth and see if radio turns off. simple problem just turn the radio off by botton in radio.

There’s no button on the steering wheel for the radio.
The problem seems to be electrical.

Later on he went out to his truck to check the battery again and noticed that the radio was powered off completely.

Seems to be a short of some kind.

With this model the time is not even on when the key is not in the ignition. His turned on and even was able to use the radio without the key in the ignition.

If power to the radio is controlled with the ground side there may be a problem there. I would check out what Boxwrench said also.

The ignition switch should be looked at also. There may be a short to the Accessory position while the key is in the Off position. By pulling the fuse for the Accessories you will be able to see if that cuts the power off.