Handbrake light comes on but fluid level is topped up

When you engage the handbrake the handbrake light should come on. It has nothing to do with the fluid level.
If it is coming on without the handbrake being applied, then you possibly have:
1. A faulty switch. The switch activates the handbrake light.
2. A stuck braking cable. To eliminate this place the handbrake on and attempt to back-up (reverse). It should not move with your foot off the brake. Do not put your foot on the gas (accelerator). Place your foot on the brake and disengage the the handbrake. Again with your feet neither on the gas or brake. The vehicle should move backwards.
In all likleyhood the switch is bad. It is easily located right under the handbrake arm and easily removed and replaced.
Let me know if this helped, or if you have any additional information, problems, or questions. Feel free to contact me at FixYa.com!

If you use your hand brake alot the cable will stretch over time. it may need to be tightened