DrKrazy Posted August 2, 2007 Share Posted August 2, 2007 Ok my 96' OBW fried an alt today on my way to work...no notice except the stereo turning off, then my speedo and tach stop workng... Luckily I have a yellow top optima in it currently (Thanks Jerry! and yea I know it's supposed to be in the rig but it's just sitting atm) which gave me enough power to get off the highway, sit at a light for a few minutes, and make it to a parking lot before it died. Called wife, had her bring me some tools, swapped it for a new one from the parts store, quick jump and I'm on my way again. Ok so after that whole ordeal was over I noticed that there IS a little battery light symbol on my dash but it doesn't light up before you start the car nor did it light up when my alt died. Guessing the bulb is burned out and probably means I have a few more burned out too and just don't know it. So if someone who know's all their lights are working could snap a pic of your dash for me with all the lights lit up (like before starting) that would be great! I can then compare and see which ones I need to replace before tearing the dash apart to replace the one. By the way I love all my older Roo's just a tad more today for having an actual voltage gauge! Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted August 2, 2007 Share Posted August 2, 2007 Hi, this is from a '96 Legacy right after turning the key to run: Quote Link to comment Share on other sites More sharing options...
DrKrazy Posted August 3, 2007 Author Share Posted August 3, 2007 Perfecto! Thanks just what I needed, looks like I'm good minus the damn battery light that would've been nice to have today! Quote Link to comment Share on other sites More sharing options...
OB99W Posted August 3, 2007 Share Posted August 3, 2007 Do you know the relationship between the "battery light", the alternator field winding, and output from the alternator? (By the way, that question was meant to stimulate thought and further discussion; I do know the answer. ) Quote Link to comment Share on other sites More sharing options...
Cougar Posted August 3, 2007 Share Posted August 3, 2007 OB99W, DrKrazy may not like to hear what you have to say about the "battery light" after he has replaced the alternator already. Quote Link to comment Share on other sites More sharing options...
OB99W Posted August 3, 2007 Share Posted August 3, 2007 Cougar, You're right; you should be the one to explain. Quote Link to comment Share on other sites More sharing options...
Bserk Posted August 3, 2007 Share Posted August 3, 2007 This reminded me of a 'very' small issue with my '96 Legacy OB.... Turn the cruise control on, and the light in the main switch lights. But set 'cruise' and no other light.. (the cruise works perfectly, just no 'cruise on' indication. Is there supposed to be one in the cluster? Maybe I have a blown bulb as well Quote Link to comment Share on other sites More sharing options...
DrKrazy Posted August 3, 2007 Author Share Posted August 3, 2007 If you have information then spit it out guys I can take it. The alt was the problem (was tested bad) and of course when I went to go start the car this morning low and behold the battery light was on in the run position so it wasn't burned out after all... But if you guys know of another problem that might be lurking plz let me know as this is my commuter car, though I'm not too concerned as it's being doing just fine since I replaced the alt (in fact a few weird quirks disappeared). Oh wait you guys talking about the fuse related to the alt? If so no worries was the first thing I checked remembered reading about it. Quote Link to comment Share on other sites More sharing options...
Cougar Posted August 4, 2007 Share Posted August 4, 2007 Cougar, You're right; you should be the one to explain. Ok, I will, since you don't want to be the one to have to do it. Sorry for the drama here DrK.. We just had a little ribbing going on at your expense. What we were eluding to is the little harmless looking battery light in the dash actually has an important function in the operation of the alternator. The current that is needed to excite the alternator field passes through that light so if the light doesn't work then the field in the alternator doesn't work and now I guess you know what that means. No output. A perfectly good alternator looks bad but really isn't. The moral of the story is if the alternator doesn't work the first thing to check is the light and make sure it works in the test mode. It turns out in your case you did need to replace it so you didn't waste your time after all. I learned this lesson years ago when I couldn't figure out why the alternator in a truck I was working on wouldn't work and I knew the alternator was ok. I spent hours working it until I finally was lead to the bulb by following the wire from the alternator. Replaced the bulb and then it worked. A lesson learned the hard way. Quote Link to comment Share on other sites More sharing options...
OB99W Posted August 4, 2007 Share Posted August 4, 2007 If you have information then spit it out guys I can take it.Sorry, I got carried away there (actually, I didn't originally have the time for a long post). As Cougar explained, the alternator field current comes through the charge light (when the engine is being started); if the light is burned out or its wiring is defective, the alternator can have no output (but see below about the brake warning light). If the alternator is okay, once the rotor is turning with the field "excited", there will be output; that output is then fed back to the field winding, so the field current no longer flows through the charge light, and the light goes out. [...]I'm not too concerned as it's being doing just fine since I replaced the alt (in fact a few weird quirks disappeared).Would one of those quirks be that the brake warning light came on, but the parking brake was off and the brake fluid level was okay? That can happen when the alternator output drops; the ground end of the brake warning light is connected (via a diode) to the alternator field winding, so that the light is tested at engine start. (In fact, it can be a secondary source for the initial field current.) Oh wait you guys talking about the fuse related to the alt? If so no worries was the first thing I checked remembered reading about it.No; I did bring up that issue recently, but it was in relation to a situation where the alternator wasn't outputting and several dash lamps weren't lighting. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted August 4, 2007 Share Posted August 4, 2007 Good info, I didn't know that about the battery light. That's a good troubleshooting tip. So the alternator field current must be pretty low then? For some reason I thought the field current was in the amps range maybe as much as 10A? Quote Link to comment Share on other sites More sharing options...
DrKrazy Posted August 4, 2007 Author Share Posted August 4, 2007 Ahh okay I understand, but damn that should be considered a weird quirk by itself! So now that my battery light is coming on in the run position there's no need for me go hunting for other problems then right? And no my weird quirks were a slightly rough idle when in drive at a stop light (that didn't show on the tach) and my ABS would do a jerk-jerk in the last few feet when coming to a stop. Both are completely gone now, so guessing that alt has been going bad since I got this car. I had just figured both of those quirks came with the 215k miles that are on this car nice to find out I was wrong. Quote Link to comment Share on other sites More sharing options...
Cougar Posted August 4, 2007 Share Posted August 4, 2007 If the light goes out while the engine is running then you should be good to go. Glad you got it working ok. There may have been some shorted output diodes that caused the trouble with the old unit. Quote Link to comment Share on other sites More sharing options...
OB99W Posted August 5, 2007 Share Posted August 5, 2007 [...]So the alternator field current must be pretty low then? For some reason I thought the field current was in the amps range maybe as much as 10A?Depends -- the higher the output current demand from the alternator, the greater the magnetic field (and therefore the greater the field current) needs to be; it can indeed be several amps given enough load. However, the initial excitation field current requirement is quite a bit lower, and the current passed by the charge light is easily sufficient for that purpose. Quote Link to comment Share on other sites More sharing options...
gbrand Posted August 5, 2007 Share Posted August 5, 2007 Good point to check alt light, I have seen this overlooked on other vehicles several times. On my 91leg when to alternator failed the light did NOT light, I found the stereo died and car began losing power just before going dead. Was on freeway bringing clutch cable home from dealer for my 80 wagon, managed to get to shoulder and wait for spouse to rescue me, jumped battery long enouogh to get home...new alt from pep boys dies 24 hours later, replacemnent lasted 8 1/2 years after that-still had recipet to get a free replacement this summer. Thinking about addding a voltmeter to give a better indication of charging system health Quote Link to comment Share on other sites More sharing options...
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