Alternator Warning Light - Diagnostic Approach

neon

neon

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Hello Fourm - In need of some help here. The red alternator warning light was coming on at low RPM, then off at about 2000 rpm. I was going to check the B + voltage but in my haste I forgot to disconnect the battery. I created a spark while trying to remove the B + terminal nut and there was a puff of smoke. Following that the alternator warning light is on at all RPM's. Presumably I shorted out and fried something - Voltage regulator ? Is the regulator within the alternator. I have been reading the blue manual but rather confusing. Thanks for any advice.

Dana Woods
 
Do you have a regulator next to the relays by the battery? If not you have a modern single wire Alt. Dimly glowing red light usually indicates brushes are worn out.
 
B+ voltage is tested at positive terminal of the battery- it’s a direct wire from alt to battery.
Don’t disconnect anything.
 
Thanks HB Chris and sfdon - I do have a regulator next to the relays by the battery, with (faded) yellow tape at the base. Strangely, when I reconnected the 3 prong plug and the B+ wire, as well as the battery, and restarted the car the light exhibited its previous behavior, on at below 2000 RPM and off at 2000 rpm and above. The B + voltage was at first about 13.4 but tehn began to vary between 12.5 and 13.1, too low.

Thanks
Dana
 
Check the three wires, usually in a plastic cover, they degrade and the insulation wears out giving you a short. I think it is your brushes.
 
HB Chris said:
Do you have a regulator next to the relays by the battery? If not you have a modern single wire Alt. Dimly glowing red light usually indicates brushes are worn out.
Click to expand...
Chris -
HB Chris said:
Check the three wires, usually in a plastic cover, they degrade and the insulation wears out giving you a short. I think it is your brushes.
Click to expand...
Thanks Chris. The insulation on the wires looks good. The diagnostics discussed in the blue manual are very complex, and difficult to decipher. Do I have to pull the alternator in order to replace the brushes ? What about the diodes - is there an easy way to test those ? I assume you are thinking that the brushes are worn due to the fact that the voltage is too low at idle but ok after 2000 rpm ?

Thanks
Dana
 
HB Chris said:
Check the three wires, usually in a plastic cover, they degrade and the insulation wears out giving you a short. I think it is your brushes.
Click to expand...
Oh forgot to mention: alt warning light does not really glow dimly, it is lit below about 1700 - 2000 rpm, then off completely above that rpm range
 
First, check all the wire connections, over time the multi strand wires tend to fracture & may have only one strand. In the past,
I've had the ground wire loop break off as I'm removing it to check. Also had one wire pull effortlessly out of the crimped connector, both of these happened after a 7,000 mile round trip aross the country!

Could buy a new Voltage Regulator, $20 if that does not remedy the issue...
Either have your alternator rebuilt or replace it with an internally regulated one & leave the old voltage regulator there for looks.
 
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Dana, On a modern Alt the diode and brushes are one unit, just two screws hold them in. I don’t remember how the early alt brushes attach. Do you have the blue books?
 
Hello, In the Autobooks supplied by this forum, Chapter 12, Page 128, There is a simple test of the voltage regulator/Alternator. Engine off, remove plug from voltage regulator and bridge the two female sockets next to each other with a jumper wire. Start vehicle and if the Alternator lite goes out and your voltmeter across the battery shows charging. it's a voltage regulator failure. If the light stays on it is a alternator failure. Do not leave jumper wire installed for too long. The alternator is running at full capacity.

Larry Louton
 
Andrew, Chris, Larry - appreciate that. Will check all the wires in detail, so far they look OK. I did see that quick test in the blue book and I think I will proceed w that

Best
Dana
 
On a side note, one of the best things I ever did to my 2002 was change over from an externally regulated alternator to a (higher power) internally regulated one.
I did the same thing on my E9. Sooooo much better in the long run.
 
adawil2002 said:
First, check all the wire connections, over time the multi strand wires tend to fracture & may have only one strand. In the past,
I've had the ground wire loop break off as I'm removing it to check. Also had one wire pull effortlessly out of the crimped connector, both of these happened after a 7,000 mile round trip aross the country!

Could buy a new Voltage Regulator, $20 if that does not remedy the issue...
Either have your alternator rebuilt or replace it with an internally regulated one & leave the old voltage regulator there for looks.
Click to expand...
Andrew - can you describe where the ground wire you are mentioning is located ? I dont see anything that looks like a ground going to the alternator - unless it is the brown wire that goes to the 3 prong plug ?
 
The e9 has no separate ground wire from the Alt to the motor as the 2002 does as it has rubber Alt mounts. Check all three wires from regulator to Alt.
 
Thanks Chris - yes I did check all three wires, there is good continuity - very low ohms, all 3 wires. Next will do the jumper test suggested above by Larry
Dana
 
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