I recently bought a 2005 F-150 and have no idea what the red flashing light means on top of the dashboard. Can anyone please enlighten me? No pun intended 😁

 

Ok button not clickable because engine size is not selected. Check my signature below to see why.

You said red light on top, is it factory or aftermarket, can you attach a screenshot?

 

If it is a little red light on the top of the dash, it might be part of the security system to warn would be thieves the security system is in that vehicle.

If it goes out once you start your vehicle, that is what it is.

 

Yes it does stop flashing when the engine is running. Here's a photo of it. Also, it;'s located directly in front of the driver seat,. It's hard to tell in the photo.
[img alt="The red light
."]https://cimg2.ibsrv.net/gimg/www.fordforum.com-vbulletin/1500x2000/red_light_b8e09987eea1d99fd66388526ef2b2e74e5fe8c9 .jpg[/img]
The red light .

 

Pic from external link tends to last only a few months.
Your pic shown below. Always attach pic here so 10 years from now it's still visible, to make this thread meaningful.

That's called sunload sensor. It's also a secondary indicator for PATS.