Alot of people have complained of the lower operating voltage the Subaru alts put out.Generally at cold start the highest voltage is seen (14.2-14.4).Quickly after warm up the voltage drops to around 13.6-13.8.By installing a diode in the alternator voltage sensor wire you can trick the alt into seeing a lower voltage than currently present.This allows for a higher voltage output from the alt.I effectively saw a .5 volt raise in voltage through out the system.This equals better performance from stereo equipment,lighting,coil packs,fuel pump.... (you get the idea) I used a 6A 1000V diode from Parts Express Parts Express:#Power Supply Diode 6A 1000V
1. Disconnect the negative (black) battery cable and hold down the brake pedal for 30 seconds.This dissipates all capacitance from the system.Be forewarned this will erase all your radio settings and realtime map setting if you use a Cobb AP.
2.Disconnect the alternator plug and cut back the wire loom.Find the blue wire with red stripe and cut it at least 3-4 inches from the plug.Install the diode with the stripe facing towards the plug.You can either solder it in place or use some butt slice conectors.
3.Now use some electrical tape to seal up the splice and reconnect the plug to the alternator.Now reconnect the negative battery cable.Thats it!Done!
Just as an update,everything still working fine!Also for a cheap upgrade as well the Forester 2.5L (NA and Turbo) alternators are 90A like the STi and are direct swaps into the 2.0L 75A WRX alternators.I picked on of Ebay a while back as a spare and I got it for $40 shipped!