Carlisle nodded in Ashley Young's free-kick and King netted after Nicky Weaver dropped Anthony McNamee's cross.
Weaver turned Matthew Spring's shot over with his foot before Ben Foster pushed Chris Brunt's free-kick around the post and denied Lee Peacock.
Young shot against Weaver's legs before Foster let Glenn Whelan's 35-yarder go through his hands in time added on.
Sheff Wed boss Paul Sturrock:
"We just can't afford to lose the type of goals we are losing, and we have to start games differently.
"When the players don't do as they are told, and they do not show commitment to the cause, I will not pick them.
"A striker was my priority - but I think we need players further back. We definitely need to get one or two in."
Watford: Foster, Doyley, Carlisle, DeMerit (Mackay 79),
Chambers, Devlin, Mahon, Spring, McNamee, King (Henderson 65),
Young (Stewart 86).
Subs Not Used: Chamberlain, Bangura.
Goals: Carlisle 17, King 24.
Sheff Wed: Weaver, Bullen (Lee 9), Wood, Diallo, Heckingbottom,
Eagles, Brunt, Whelan, O'Brien, Peacock, Graham (Agbonlahor 63).
Subs Not Used: Partridge, Adamson, Rocastle.
Goals: Whelan 90.
Ref: B Curson (Leicestershire).