so on the way to church yesterday morning, my wife had the brake (parking brake) and battery voltage lights come on in our 2002 legacy 2.5 GT.

 

i brought it home, checked the battery terminals, etc. nothing wrong there. took it up to advance, where they ran a load test on the alternator and electrical system. came back that the system voltage was low, either bad alternator or wiring problem.

 

so i took the alternator off to have it bench tested. 3 different benches registered the alt as good.

 

put it back on, and check it with my multimeter. alternator has 3.7 ohms of resistance between it and the negative battery terminal. so the alt itself has a good ground. .1 ohm of resistance between the charge wire and positive battery terminal. no jiggling, bending, etc of the wire changed the resistance, so I'm pretty sure where good there.

the light blue and red wire has full battery voltage with the key off, just like the factory service manual says it should. the black/white wire has full battery voltage with the key in the run position like it should, even with the car running.

 

when i first fired it up to see if the alternator was putting out while in the car, i had a full 14.7 volts at the charge post. it quickly dropped to 12/3, battery voltage. cant make it come back up to charge voltage again.

 

so, what the hell am i missing here? alternator checks good, I'm getting voltage where/when i should, connections and grounds are clean and tight, etc.

 

 

all i can think of is that i may have a bad cluster. in my factory service manual, it shows a diode between the brake warning light circuit and the voltage light circuit. I'm assuming that's why the pair came on simultaneously.

 

any ideas, guys? I've been puttering around with it for 2 days now, and its time to ask for help.

 

Michael

sounds clearly like a faulty alternator.. the battery should never go down to 12V while running

 

Also the first two signs of this issue is the brake and battery lights come on.

Voltage that low when running means the alternator is not charging as it should. If you have a local re-builder that might be the most cost effective option. Auto parts store alternators can be hit or miss. A Subaru reman unit is generally the best as far as quality is concerned, but dealer parts are $$$.

Don't know for sure as I don't have much experience on the newer models.

 

But on the older ones when the alternator would start to go the ABS light and another seemingly unrealted light would come on. Drive long enough and you often loose the high RPM range as you are running off the battery. Eventually you stop.

 

I typed this but wasn't gonna post it since I haven't had this issue on a newer moddle - usually I stop at '99.

 

Since other have posted basically the same thing I'd thought.

 

In short I wouldn't trust the test. Or perhaps take it to a "real" electrical shop that actually rebuilds starters and alternators.

I had an alternator go intermittent on me for a few days, then totally quit out. Brake and batt light, low voltage. It turned out to be the the wire that goes to one of the brushes broke. About three weeks after that being fixed the regulator started to go. It would only put out over 1000 RPMs, then 1500, then 2000... you get the idea, just got worse and worse.

Altenator. Bench test is useless and a waste of everyones time.

 

You are missing the proper test actually.

 

start the car and rev it to 1800RPM or more.

Turn EVERYTHING on, and i do mean everything.

Take the voltage reading.

 

Don't by the cheapest rebuild you can find, you will regret it.

Edited March 8, 201115 yr by nipper

I just went through this with my car, its not that new tho. But anyways i did everything u just described that u did to ur alternator then i finaly just broke down cuz i was tired of it happening and bought a new alternator because it was only $140 for a new one with a lifetime warranty for asnlong as i own my car from napa compared to the cheapest place i could get mine rebuilt at for $90. But i can almost say for sure its the alternator.

After reading you post here are some things that stood out to me.

 

You stated you had 3.7 ohms of resistance between the alternator and the negative side of the battery. I'm not sure where the meter probe was at on the alternator. If you were on the case of the alternator then there is a problem with the battery ground. You should see zero ohms of resistance. If you are taking about the output lead of the alternator then that isn't right either.

 

You also stated the voltage dropped down at the battery after you started ithe engine. You need to see what the voltage was at the output lead of the alternator. If it is 14 volts and the battery side is lower then there is a wiring problem between the alternator output lead and the battery.

 

As a note. The warning lights are in the field lead circuit of the alternator and that is why they can turn on when the alternator has a problem.

Edited March 8, 201115 yr by Cougar

so i got the ohm reading from the alternator case to the battery ground down to 1 ohm. still had the light. put a reman alternator on it, and the lights are off, the high beams dont dim anymore at idle when the radiator fan kicks on with it in gear. still getting a 12.87 volt reading at the alternator charge post with all the electricla accessories on max, at idle, in gear. odd to me, but.....

 

im going to drive it A LOT tomorrow, and see what happens.

any other ideas, or if the lights dont come back on assum ive got it and stop thinking about it?

 

Michael

Nipper suggested doing the loaded voltage check at 1800 RPM not idle.

 

You probably have it fixed. May want to check your battery too as it has been discharged a lot recently. If its fairly new (couple of years) its probably ok.

If you have about the same voltage at the battery as the alternator output post then it sounds like you have things under control.