OK all, I’ve searched on this and found some info, but I’m still confused…..

I am planning on installing a high-output alternator in my 2003 WRX. In addition to a connection to the OEM alternator wiring harness, there is a wire coming out of the high-output alternator that I need to tap into my ignition wire. I am not absolutely sure why the alternator needs an ignition lead, but I am assuming it tells the alternator when to start/stop powering the car’s electrical system.

Although the draw on this ignition lead will probably be pretty small, I want to hard wire it to the battery to avoid too much draw on the OEM wiring. So I’ll need to incorporate a Bosch relay to do so, and I’m confused on how the wiring should be configured. Here’s how I think the wiring should go (based on my search results):

Pin 30: Battery positive (fused)
Pin 85: Ground to chassis
Pin 86: Tapped into ignition lead (i.e. switched)
Pin 87: To alternator
Pine 87a: Unused

Can any wiring gurus verify that this is the correct configuration? Thanks in advance!

You're correct on both counts. The alternator needs the ignition lead to tell it when to turn on.

You're also correct on the pins for the relay. I made a diagram a while back showing the pins for a relay and how they work. It may be helpful for future reference.

http://www.surrealmirage.com/subaru/tip.html#relay

Josh

Josh - Thanks for the info. Just what I was looking for.....

welcome