This will depend 100% on what tail lights are installed in you Step Van, Chevy did not make the body, many other companies did.
So who built your body?
How do you replace a break light switch on 1995 Chevy Tahoe
check you brake fluid level.
Your brake light is probably brake fluid low or emergency brake on. Rear brake lights are replaced by removing the lens and replacing the dual filament bulb.
Its located on the brake pedal. Unplug the wiring harness and unbolt it and replace it.
replace the sensor behind brake paddle.
the screws come off and you replace it
carefully
buy a tap and die set.
Located at the upper end of the brake pedal under dash area
To replace the brake light on a 1995 Toyota Tercel, first, open the trunk and remove the plastic cover or trim panel on the side where the brake light is located. Then, unscrew the brake light assembly, disconnect the wiring harness, and remove the old bulb by twisting it counterclockwise. Insert the new bulb, reconnect the wiring, reassemble the brake light housing, and finally test the new light to ensure it’s working properly.
Check the fuse, check the bulbs and check the brake light switch, it should be one of those.
Bulb is probably defective. Replace it.