QUOTE(Tom @ Mar 18 2012, 04:49 PM)
Your testing the alternator with on ohmmeter sounds correct. Diodes will read one way, not the other if they are good. Although this is not a test that proves them good all of the time. They sometimes can break down under load.
Here is what I would do. Charge up the battery , hook everything up like it should be and test the battery voltage when off and when running. Off should be same voltage as battery voltage after charging, on and running should be 13 - 14 volts. If this is good, alternator is probably OK.
Now ( step 1), disconnect the 4 red wires at the + battery terminal and leave overnight. If the battery is good it means you have a drain in your power to the key switch, fuse panel under dash, or relay board or alternator. If battery is still bad, ( step 2) disconnect the neg battery post, charge it up and leave overnight. If battery is bad then, you have a bad battery.
If after step 2 the battery is OK, then disconnect the large alternator lead at the starter and insulate it, hook up the battery neg and positive terminals and let it set overnight. If battery now is bad, you have something causing a current draw in the alternator.
Hope this helps get you through this.
Tom
Thanks Tom,
Last night the battery was unplugged and it now starts right up.
Ok, Battery is charged with 12v. With car running I get 14.5v.
The one failed test I saw at O'Reiles was an over charge.
The load I read on the multimeter with everything hooked up and with the dial on Rx10, the needle reads 5. I don't know, is that a lot?
Disconnect the alternator and it reads about 30.
The car has 90% Subaru wiring, ECU, and gauge cluster.
The WRX gauge cluster is not showing a charging or battery problem.
The car will sit over night with the alternator unplugged.