I agree with Beth in reference to the need to strip and also with Jim in reference to the possibility of residual staining.
You may very well have to strip more than once, and carefully, due to the delicate nature of the shakes.
The photographs below are of 20+ year old siding on a garage located at 5500' elevation in the Arizona mountains.
The side with the garage doors faces almost due East and the other side faces Southwest and is fully exposed to the sun. We also restored the oak garage doors.
There was some residual staining remaining after stripping, so we decided to go with a blend of 2 parts A/C Cedar-Semi and one part A/C Cedar tone.
The renovation was completed almost 2 1/2 years ago.