can I install Sell Support Assist on my D: drive

You cannot typically install Dell SupportAssist on your D: drive; it's designed to be installed on the C: drive (where your operating system is installed) and its default location is C:\\Program Files (x86)\\Dell\\SupportAssist\\
SupportAssist is designed to be installed in the system's main drive (usually C:) and not on other drives like D:. 
The software needs to be accessible by the operating system and its core functions, which are located on the C: drive. 

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Same problem for me. When I set up my SSD, I allocated 120 GB to the C: drive. Today, the Dell suite takes up most of that space. How can I make sure this is not the case. So much wasted space, generating repeated space shortage alerts for and by... Dell Assist Support.