Relay clicks under dash, have to use starting fluid

[Stroken49s]

My brother has a 00 7.3 that has 200K on it, and sometimes it will start cold just fine, but when he hears a relay clicking under the dash, it wont start and he has to use starting fluid. Anyone else had this problem or know of a fix, he changed the relay out and still does the same thing Thanks in advance.

[WackerCattle]

When mine clicks under the dash, it's usually low on charge, probably won't power the glow plugs?? When it does that, look at the amp gage, see if it's below 8.