In the post on the confusion on identifying father and son, and who owned which regiment, this post will deal with the regiments.
The later 1st Earl of Macclesfield would command the 1st Troop of Horse Guard, or His Majesty's Own Life Guards, between 17 May 1660 and 16 September 1668.
Late 1677/early 1678 England had switched from a pro-French to an anti-French attitude. As such, England was about to take active part in the Franco - Dutch War, on the side of the Dutch Republic. One of the new regiments levied for this war was Lord Gerard's Regiment of Horse, with the commission for Charles Gerard, who was to become 1st Earl of Macclesfield in 1679, signed 15 February 1678. This regiment was disbanded in January and March 1679.
Another regiment embodied for this war was a regiment of horse commanded by the Duke of Monmouth. Though it was also disbanded after the Treaty of Nijmegen, it appears that the regiment was re-formed in June 1679 during the Covenanter Rebellion, with Lord Gerard, the son of the Lord Gerard above, as colonel. The regiment was disbanded later in 1679.
As has been detailed in the other posting on the Earls of Macclesfield, the son remained loyal to James II whereas the father had to go into exile. In 1688 we see him in command of a new regiment of horse, Lord Brandon's Regiment of Horse, dated 1 October 1688. This regiment was disbanded on 4 January 1689.
In 1694 the son, who had succeeded his father as 2nd Earl of Macclesfield by this time, raised a new regiment The Earl of Macclesfield's Regiment of Horse, dates 16 February 1694. This regiment survived the reductions after the Treaty of Rijswijk, but was finally disbanded in 1712.