If you find it strange to have 4 brightness settings, and feel you only need off, medium and bright, it is possible.

Enter unit into developer mode. Plug it into your PC and then navigate to the mass storage drive for the GPS.

Navigate to APP>mgnShell

Look for brightness.dat, open it in word pad.

You will see 2 lines. One for normal and one for low power.

I change min to 10,73,99 for normal which is off, medium and max.
I set low power to 10,73,85 this just makes the brightest setting a little less then max to save power.

Save the file.

When you restart your unit you will find that there are only 3 settings.

You can also set it for just off and on. Or you can make as many settings as you want.

This is pretty old, isn't it?

If you want to make the dimmest setting dimmer, the lowest setting it recognizes is 66...

It will recognize even lower. But the backlight is starting to flicker.

Humm... If its old, how come its not in this section already??

... maybe, because it is not a classical easter egg: a feature which showed up when you type a special sequence of keys ...

The way to control the brightness is previously mentioned here!
(You will recognize the author )

Regards
Dirk