The US helped and quite probably decisively.
They gave us 100 of the then latest model Sidewinder missile AIM-9L which even the USAAF hadn't yet got fully into service at the time.
These could be fired from any angle and could home in on the heat friction on a wings leading edge, not just a tailpipe, which became very important when dealing with the Mirages in the very small time slots of engagement which didn't give much opportunity for niceties like maneuvering behind the target for a kill.
17 known kills and 2 assisted kills for the Sea Harriers. These AIM-9L's were even put on the Nimrods.
They also gave us Shrike for Anti Radar strikes, that Vulcan that had to put down in Rio de Janeiro after the refuelling probe broke even had two under the wings which was slightly embarrassing. The Vulcan strikes were also meant to loose these off if they got lit up by the Argentine mobile radar sets to knock them off before the eventual landings.
Stingers were also supplied to the special forces and used successfully.
I think the US even offered us a loan of recently de-commisioned fixed wing carrier but we had to refuse as our fixed wing RN experience had withered badly and the Phantoms & Buccaneers had been de-navalised, arrestor gear off etc. If I'm not mistaken, and I had an impeccable source, there was also a big gas laser for blinding hurriedly fitted on Invincible somewhere down south but that's all a bit of a mystery that no one ever speaks about.
Certainly US Satellite intel was flowing quite sweetly to those who needed it.
I'm also pretty certain that LGB's were used right towards the end on some Argentine artillery positions outside Stanley, but I'm not sure if the ground based laser target illuminators & the munition guidance packages were US supplied or if we already had them.