The B741 road between New Cumnock and Dalmellington is set to be closed for three weeks from next month.
Scottish Power work will be carried out on the road, forcing a full closure in both directions.
The road was also closed for one day back in June, but more extensive work is being carried out this time, with a 35-mile diversion in place.
A closure is set to be in place from 7am on Tuesday, September 10 until 5pm on Wednesday, October 2.
Emergency service access will be maintained, with a separate diversion in place for high-sided vehicles, due to the railway bridge near Coalhall.
A diversion will be in place from Dalmellington, via Ayr Road A713, B742, A70, A76 and vice versa.
The high-sided vehicle diversion will via Ayr Road A713, B742, A70, B730, B7046, U728 ,A70, A76 and vice versa.
More information about the diversion can be found on the Ayrshire Roads Alliance website.
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