Action at the Winton Supercars test has come to a pause due to a shower at the regional Victorian circuit.

Rain started to fall at around 14:10 local time/AEST, followed by a brief closure of pit exit.

While the green light is now back on at the end of the lane, no one has opted to venture back out, with Tickford Racing and Walkinshaw Andretti United taking a wait-and-see approach on the weather.

It means 12 Gen3 Mustang drivers are waiting in their garages, with each of those teams having their full complement of enduro co-drivers on hand today.

Meanwhile, contrary to an earlier report, Speedcafe has now learnt that all six Mustangs at Winton are in fact running the new-spec 80mm throttle body.

However, they may still be in somewhat different engine specs overall, with some cars thought to be running different throttle translation tables to others.

For both WAU and Tickford, this is also the first test day with the new rear aerodynamics which debuted in competition last time out at the NTI Townsville 500.

Update 15:32 AEST

All four Tickford cars and the #2 WAU entry have gone back out, onto a damp track, with at least three of the former known to be running on wets.