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.
Its located on the brake pedal. Unplug the wiring harness and unbolt it and replace it.
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.
replace the sensor behind brake paddle.
the screws come off and you replace it
carefully
Located at the upper end of the brake pedal under dash area
buy a tap and die set.
Check the fuse, check the bulbs and check the brake light switch, it should be one of those.
Bulb is probably defective. Replace it.
Why not just remove the bad bulb and look see what model it is?