Interesting Electrical Discovery

[BrentBTK]

When I installed my new engine, it came with a one wire alternator. Because I just wasn't sure, I also connected the brown "alternator" wire from the American Auto wiring harness to the same post. Out of curiosity, I disconnected that small wire today to see if it made a difference. It did not. UNTIL... I shut the truck down and the electric fans that had previously run after it was off no longer do. Apparently the "electric fan" wire in the AAW wiring harness gets its power from that wire. Makes me wonder what else might. Clock still works. I don't think the fans shutting off with the truck are an issue, correct me if I'm wrong. Mechanical fans don't continue to spin...I kinda prefer it this way, honestly.

[pjmoreland]

That brown wire comes from your ignition switch, so you were back-feeding your electrical system by piggybacking it onto the other alternator wire that is always live.

[BrentBTK]

Originally Posted by pjmoreland

That brown wire comes from your ignition switch, so you were back-feeding your electrical system by piggybacking it onto the other alternator wire that is always live.

That makes sense. So I'm guessing the fans are ignition controlled after all, and I was just forcing that circuit to be constantly hot.

[pjmoreland]

We at least partially hot because that brown wire has higher resistance than a normal wire.

[RustyPile]

Originally Posted by BrentBTK

That makes sense. So I'm guessing the fans are ignition controlled after all, and I was just forcing that circuit to be constantly hot.

That brown wire is used exclusively for a conventional internally regulated alternator.. If you insist on using (I don't recommend it) that one wire alternator, leave that brown wire disconnected.. Keep this in mind in doing so.. It's not a good idea to leave a disconnected live wire running loose in a wiring harness.

Countless posts and threads (pro and con) have been made about those one wire alternators. If you're interested in learning, do some searching on this site and learn about them..