Jenson Button steered his repaired McLaren to the fastest lap on Wednesday, and Nico Rosberg helped Mercedes rebound from Lewis Hamilton's crash with the longest run on the second day of Formula One pre-season testing.
Otherwise, most teams continued to struggle with their new cars following a massive rulebook overhaul that includes a shift to a turbo engine and more sophisticated energy recovery systems.
Four-time defending world champion Sebastian Vettel only managed eight laps around the Jerez track before Red Bull's engine maker, Renault, reported a malfunction and the team decided to call it quits. That gave Vettel a total of 11 laps to start the preseason.
"Obviously we've not had a lot of running and have a few problems to sort out, but with such big rule changes it is usual to have some teething problems. That's what tests are for, to sort those issues out," said Vettel, who now hands the wheel to new teammate Daniel Ricciardo for the remaining two days in southern Spain.
An electrical problem had kept Button in the garage on Tuesday, but he was the first out on wet tyres in the morning and after the asphalt had dried he set the benchmark lap time with 1 minute, 24.165 seconds.
The former world champion is aiming to help McLaren bounce back from its worst season since 1980 after it didn't reach the podium last year.
Rosberg led the eight-car field with 97 laps, a day after a front wing problem sent Hamilton's Mercedes flying into the barrier.
Rosberg said the new Mercedes F1 W05 has little in common with its predecessor and compared its steering wheel to a "smartphone with all the information on it."
After overnight rain, the session's 9 a.m. start was delayed as a tractor worked its way around the track spraying more water on the already damp asphalt so teams could test Pirelli's tyres for wet surfaces. But by noon the sun had come out and the track was dry as forecasts of showers never materialised, leaving teams to run under normal conditions.
All the teams are struggling to get their cars race ready in time for the season-opening Australian Grand Prix on March 16. They will have two more tests in Bahrain before heading to Melbourne.
So far, they have combined for 424 laps across two days of testing. Last year, with the pre-season starting after far fewer tweaks to the rules governing car design, drivers combined for more than 1,500 laps over the first two days here.
Ferrari appears to be handling the new regulations the best. Kimi Raikkonen followed up his fastest lap time from Tuesday with the second-fastest lap on Wednesday, 0.647 seconds behind Button. Local favourite Fernando Alonso will drive for Ferrari on Thursday and Friday.
McLaren's promising recovery from Tuesday's no-show coincided with its hiring of Eric Boullier as its new racing director. Boullier joins a week after leaving rival Lotus, in a restructuring at McLaren that recently included luring back former team principal Ron Dennis as its new chief executive.
F1 newcomer Marcus Ericsson came to a stop in his Caterham for the day's third and final red flag. Sergio Perez's Force India had spouted smoke earlier after Esteban Gutierrez ended up in the gravel in his Sauber.
F1's new rules include a shift to a 1.6-litre V6 turbo engine from last year's 2.4-litre V8. They also affect the cars' fuel limits, weight and body design.