Garmin GPS 12xl

The Liquid Crystal Display on your 12xl is affected by various things, the most common of them is voltage and temperature, low (battery) voltage would result in lighter display and high voltage (supply/battery) voltage, which is fairly unlikeky, would result in darker display. Temperature will also affect the display with low temperatures usually resulting in a lighter appearance and higher temperatures resulting in darker displays

 

The backlight is only required in low ambient light (when there in no daylight), If you can't see the display during daylight, I would say the backlight isn't the problem.

Modern units tend to have LED backlights that usually last for the life of the product, however 12xl is probably 20 years old and may have a real 'bulb', I guess this is replaceable, although it may be fixed into the display permanently, in which case you would need a new display. I would say it could only be replaced by Garmin, unless you are familiar with electronics repairs

 

I'm still not clear what the problem is, when viewing in daylight outdoors what is the colour of the display? is the whole display black or dark? If not, what colour is the text and what colour is the background? can you take a photograph of the display ?

You may find a phone repair guy won't want to take it apart, it is glued together

 

Ah OK, now we're getting somewhere, this is not a backlight fault, the display is set to maximum contrast, if you can see pages change (viewed at an angle) when 'Page' is pressed, I would say the unit is working correctly, but that the display has a fault which is setting every pixel to maximum contrast, if the contrast can't be reduced from Menu >> System Setup, I would say the display needs to be changed