The service manual is clearer (for me, anyhow) on what gets powered when. I'm attaching it here - clock is on page 15.
Oh, my apologies. That's actually from the '90 service manual. I was thinking it was '88 since I have the file in the same folder as Jim's '88 color coded diagram (I don't think he made a '90 version). I think it should be the same in this area but not 100% sure.
edit: yeah it's the same connector so I do think it's the same between '88 and '90. Connector G84B.