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cheeseisgood
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Joined: October 18, 2004
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 Posted: Wed Sep 04, 2013 1:22 pm Post subject: BAT and OXS light on and blue wire question |
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So my BAT and OXS lights have been stuck on for a while since I had and intermittent alternator failure.....stopped charging, got stuck then started working again. I am getting ready to attempt to pass smog and want to get this resolved. I checked the blue wire voltage and it is only 6.7 volts when running. Voltage at bat and alt are 13+. If I connect the lead to the indicator light to 12 volts it goes out. Is this a faulty alternator? Alt is a Napa alt with lifetime warranty so not a big deal if it is.
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crazyvwvanman
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| Posted: Wed Sep 04, 2013 1:54 pm Post subject: Re: BAT and OXS light on and blue wire question |
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Where exactly did you measure the voltage on the blue wire?
Where exactly did you connect the lead to the indicator light to 12 volts?
Mark
| cheeseisgood wrote: |
| So my BAT and OXS lights have been stuck on for a while since I had and intermittent alternator failure.....stopped charging, got stuck then started working again. I am getting ready to attempt to pass smog and want to get this resolved. I checked the blue wire voltage and it is only 6.7 volts when running. Voltage at bat and alt are 13+. If I connect the lead to the indicator light to 12 volts it goes out. Is this a faulty alternator? Alt is a Napa alt with lifetime warranty so not a big deal if it is. |
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cheeseisgood
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| Posted: Wed Sep 04, 2013 2:11 pm Post subject: |
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checked the voltage of blue wire coming out of the alt at the alt.
connected to 12v at the alt.....so technically around 13v
also, both BAT and OXS stay lit if blue wire is disconnected, but as said before, go out when touched to the 12v at the alternator.
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cheeseisgood
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| Posted: Wed Sep 04, 2013 7:12 pm Post subject: |
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Update. Actually no voltage coming from the blue wire on the alt....the voltage(about 7.5v) is coming from the wire going to the light when the key is on. When key is off there is no voltage and the wire is not grounded.
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cheeseisgood
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| Posted: Thu Sep 05, 2013 2:09 pm Post subject: |
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Anyone?
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kamzcab86
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| Posted: Thu Sep 05, 2013 4:21 pm Post subject: |
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| cheeseisgood wrote: |
| Actually no voltage coming from the blue wire on the alt....the voltage(about 7.5v) is coming from the wire going to the light when the key is on. When key is off there is no voltage and the wire is not grounded. |
Is the blue wire connected to the D+ terminal on the alt? When you read this 7.5v (or 0v), have you rev'd the engine up to 1600+ rpm and then let it drop back to idle, or are you just turning the key and letting it idle? If the latter, rev the engine, then check it.
On an '87, there is a ground to the exciter circuit; it's via the OXS counter box and is at the star ground cluster above/behind the relay panel. So, check your grounds and clean them if need be.
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"Real knowledge is to know the extent of one's ignorance." - 孔子 |
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crazyvwvanman
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Joined: January 28, 2008
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| Posted: Thu Sep 05, 2013 4:49 pm Post subject: |
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It kinda sounds like an alternator problem. Tracking down electrical issues that people have often requires very detailed and exact data. When people don't seem to give it I sometimes wander off rather than pull teeth to get it.
I wouldn't concern myself with the dash ground cluster as a root of cause of your problem. Something added to the blue wire circuit it may be complicating the diagnosis but I lean toward an alternator issue. I would try unhooking the battery ground cable, removing the alternator brush/reg assembly, slightly stretching the 2 brush leads, and putting it all back.
Mark
| cheeseisgood wrote: |
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cheeseisgood
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| Posted: Fri Sep 06, 2013 11:48 am Post subject: |
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what voltage should I be getting from the blue wire running to the light with the ignition on and the blue wire disconnected from the alt?
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spacecadet
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| Posted: Fri Sep 06, 2013 12:05 pm Post subject: |
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I have a flickering alternator light after installing a rebuilt Bosch.. I was told the brushes might have been worn out too much causing this. I have a brand new alternator, just arrived today, will report back if this in fact fixes the light.
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1990 Volvo 740 Turbo(Sold)
1986 Mercedes 300 Coupe (Sold)
1954 Volvo PV544 (Sold)
1990 Dodge D250 Cummins (Totaled)
1990 Vanagon GL 2.1 Automatic (Sold)
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cheeseisgood
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| Posted: Fri Sep 06, 2013 12:50 pm Post subject: |
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I doubt that it is brushes since the alt was replaced about 5 months ago. Like I said, it has a lifetime warranty from Napa so it is free to replace so cost is not a factor, but I want to try and rule out any issue on why it failed so soon other than just a crappy rebuilt alt.
What voltage should I see from the following:
Blue wire running to the indicator light under when it is NOT connected to the alternator when the key is on
Blue wire running to the indicator light under when it is NOT connected to the alternator when the engine is running
Blue wire coming out of Alt when NOT connected to indicator light
Thanks for the help and patience!
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crazyvwvanman
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| Posted: Fri Sep 06, 2013 1:38 pm Post subject: |
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There are no fixed answers to some of your questions about the blue wire voltage. Because there are various other things connected to the blue wire circuit of the dash in models with certain options the voltages measured on the blue wire will be lower in some vans than in others. The alternator works normally in spite of this voltage variation but it may need to be revved up slightly for the dash light to go out. These same options can cause the alt/bat light to behave differently under different conditions in different vans so what someone tells you theirs does won't necessarily match what yours should do.
Mark
| cheeseisgood wrote: |
I doubt that it is brushes since the alt was replaced about 5 months ago. Like I said, it has a lifetime warranty from Napa so it is free to replace so cost is not a factor, but I want to try and rule out any issue on why it failed so soon other than just a crappy rebuilt alt.
What voltage should I see from the following:
Blue wire running to the indicator light under when it is NOT connected to the alternator when the key is on
Blue wire running to the indicator light under when it is NOT connected to the alternator when the engine is running
Blue wire coming out of Alt when NOT connected to indicator light
Thanks for the help and patience! |
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spacecadet
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Location: San Francisco
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| Posted: Fri Sep 06, 2013 2:29 pm Post subject: |
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Update: Replaced my alt and the flicker went away, both were from the same supplier, one was a rebuild: crap brushes I suppose.. the replacement is new and is working as intended..
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Daily Drivers Only
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1990 Volvo 740 Turbo(Sold)
1986 Mercedes 300 Coupe (Sold)
1954 Volvo PV544 (Sold)
1990 Dodge D250 Cummins (Totaled)
1990 Vanagon GL 2.1 Automatic (Sold)
1968 Ford F250(Current) |
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kamzcab86
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| Posted: Fri Sep 06, 2013 6:50 pm Post subject: |
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| cheeseisgood wrote: |
| What voltage should I see from the following: |
Perhaps an explanation as to how this circuit works is in order...
"The Bosch alternator is incapable of self-excitation, or "boot-strapping" itself to an operating condition. Older DC generators and some U.S. alternators have residual magnetism retained in the core, or some other scheme to get enough field current to get themselves up and running. The Bosch alternator uses a different scheme. The charge warning lamp is connected between the ignition switch and the D+ terminal. When the car is first started, there is no output from the alternator at either the B+ or D+ terminals. The voltage regulator, sensing no output, is attempting to command maximum field current... it effectively shorts the D+ and DF terminals together. This places the D+ terminal close to ground potential, because the resistance of the field winding is not large. This means that there is +12 volts on one side of the charge warning lamp, and the other side of the lamp is grounded through the alternator field winding. Current thus flows through the lamp, lighting it. This same current, however, also flows through the alternator field winding, producing a magnetic field. This magnetic field is what the alternator needs to start up, and if everything is working correctly, that's exactly what happens. The alternator now begins to develop identical voltages at the D+ and B+ terminals. The D+ terminal is connected to one end of the charge warning lamp, while the other end of the lamp is connected to the battery via the ignition switch. Since the B+ terminal is hard-wired to the battery, and since both the D+ and B+ diodes are fed from the same set of windings in the alternator, no voltage difference can exist between these two points. The warning lamp goes out.
The voltage regulator "watches" the voltage at the D+ point, which should be the same as that applied to the battery. It now changes the short between the D+ and DF terminals into a variable resistance. This effectively controls the field current (whose source is now the output from the D+ terminal, and not the charge warning lamp) and thus regulates the output voltage of the alternator." ~Jim T. at Pelican Parts
In other words, provided everything is operating & connected properly:
Key on, engine off = blue wire is a ground, light is on
Key on, engine started = blue wire is a ground, light is on
Key on, engine rev'd = magnetic field excited due to the higher rpms, blue wire is now positive, light goes out, alternator is charging
So, I shall repeat myself:
Is the blue wire firmly connected to the D+ terminal on the alternator?
Have you rev'd the engine during any of these tests?
If the answer is "yes" to both those questions and the lights remain lit, then it might be time to have the alt tested.
_________________
~Kamz
1986 Cabriolet: www.Cabby-Info.com
1990 Vanagon Westfalia: Old Blue's Blog
2016 Golf GTI S
"Real knowledge is to know the extent of one's ignorance." - 孔子 |
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cheeseisgood
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| Posted: Tue Sep 10, 2013 11:58 am Post subject: |
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Dumbass alert......blue wire at alt was actually the W wire. I believe all is good with the alt and lights now.
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