Relay Indicator?
 

I have asked this question of Ford Parts and have yet to receive an answer; What is the white opaque area on the top of the 20 A FoMoCo 5M5T-14B089-AA relay? Is this an indicator that the relay is defective or blown?
https://cimg1.ibsrv.net/gimg/www.for...685eb652a4.jpg

No idea, relays don't blew like fuse though. What is the reason you are asking?

Can we ask where was this relay and on what type vehicle?

2000 Ford Taurus 3.0 L OHV and for the fuel pump circuit.

I'm asking because I am curious, and when a car doesn't start, it would be nice if the relay "indicates" that the fuel circuit is the problem, i.e. a defective fuel pump and/or because of inadequate pressure.

Believe it or not, relays don't usually give much trouble.
They just "relay "the command/signal from the point of origin to the component.
Unfortunately, they haven't invented the tool to tell us exactly what is wrong , how to fix it and actually do the work. Maybe , someday.
They do help us by providing a code many times that ONLY tells us what system has a problem. It still requires some knowledgeable info of how the system is supposed to work and how to check for malfunctions. Sometimes it can get a bit complicated.

Relay Changed Because Fuel Pump Defective
 

I replaced the original Ford relay because after overhauling the engine the car wouldn't turn over. I knew I had spark because I replaced the components that produce spark (battery, coil pack, plugs, wires, etc.). Thinking fuel pump, I replaced the relay and, voilà, it started! It ran for a few hundred miles until, one day, it stopped IN THE MIDDLE of an intersection! Apparently the fuel pump was only intermittently supplying adequate pressure, and changing the relay was coincidental. I later tested the original relay and it tested good, however, if the original relay would have had a "good-bad" indicator (or possibly a window indicating status), then I would have known it was not the relay but an intermittent fuel pump. That's the reason for my question regarding the opaque window on the replacement relay.