I noticed this was your first post here. Welcome.
Kristin makes a good point about the parts - this function was shown in the PA39 POH.
Not sure this will help but - I have a list from 1987 of pa30/39 STCs from my Mom's files as she owned the 39 at the time.
It shows STC SA4295SW holder Crow Aviation. I googled that and found the FAA link
http://rgl.faa.gov/Regulatory_and_Guida ... enDocument
Looks like it will take more detective work to find it but this is a start. If you find it, please post here. Thanks in advance and good luck.