[6] The FW04 suffered from overheating issues and fuel pick up problems, so Head redesigned both systems at short notice, which greatly improved performance.

A race of attrition benefitted Laffite and he brought the car home second for Frank Williams' best ever result to that point.

[9] The timing was financially good as it kept the cash strapped outfit solvent, although it would be the team's only finish in the points all season.

[11] In 1976, both FW04s were sold to Australian driver Brian McGuire, who raced them in the Shellsport International Series, winning one round at Thruxton.

[13] On its debut in Spain, the FW04 was driven by Italian Arturo Merzario with young British driver Tony Brise in the FW03 on a one-race deal.

[16] In Sweden, Laffite was absent again as he was driving in Formula Two, and Merzario had left the team, so Damien Magee and Ian Scheckter were brought in to replace them.

[25] Williams finished the season in ninth place in the Constructors' Championship with six points, and all had been scored by Laffite in the FW04 in Germany.

McGuire started from pole position and secured the fastest lap of the race on his way to victory, the first time a Williams car had managed any of these feats.

[28] He also entered the car in the 1976 BRDC International Trophy in April, qualifying last and being black-flagged in the race after losing oil on the circuit.

[29] McGuire's FW04 also appeared at the 1976 Spanish Grand Prix in early May, driven by local driver Emilio Zapico, entered under the Mapfre–Williams team name.

[32] He subsequently bought the second FW04 from Wolf–Williams, the car that Lella Lombardi had driven at the 1975 United States Grand Prix,[33] while continuing to run chassis "01" in the Shellsport Series.

[34] He then entered chassis "01" in the 1977 British Grand Prix and this time was allowed to take part, but he failed to progress beyond the special pre-qualifying session.

During a practice run for this race, the FW04 / BM1 left the track and hit the barriers, killing McGuire and a fire marshal.