I'm making my own harness and didnt think to check before soldering on the connector, but are there any unused pins that I could use for extras like boost control or shift lights? I'd like to keep everything on the
connector if possible rather than running stray wires out of the box.

 

Yes, there are extras. I think SPR1-4 are un-used, as well as some of the IAC ones (on a miata setup, anyway...). Use a multi-tester to figure out which pins the solder pads connect to. If you're running MS-II, I think a couple of the SPR ones are used for CAN bus.

-Mike

 

there are a bunch that aren't used. at least 15