Only sti specific stuff I know of is DCCD and G-force sensors.   working on some PCB design bits and updating to use the newer canbus chips.   Adding a thermocouple circuit as a test and they cost way to much.

Something rectangle that sits in the top 1/3rd of the vents would be cool, like a P3 gauge but with more specialised info available. Having DCCD there would be cool 

f*** it just get one from Pickapart, they're like $40.

Likely the alternator has a replaceable rectifier unit inside. some can even be disassembled and individual diodes replaced.    

Battery tests fine, no resistance between battery posts when its disconnected from the car i only get resistance of 15ohms when i disconnect the +ve lead and test between +ve lead (not battery post) and negative  lead but yeah i realise thats f***ed haha, thats why as soon as i tested it i was like arrrrrrrr that not good    Yeah i might just order a new alternator to rule it out - heres hoping i can find one haha