<polymorph@polyphoto.com> wrote in message
news:1134167585.133582.158440@g43g2000cwa.googlegr oups.com...
> 1991 Honda Accord LX, 2200cc engine, 4 door sedan with standard
> transmission.
>
> The charge light came on one day, went on and off again, finally came
> on and stayed on.
>
> Frustrating... after checking all the wiring, removing and retightening
> the battery cables and the wires on the alternator, checking ground,
> the light went out. Thought I'd fixed it. In the time it took to pack
> up all my tools, went back and started it and the light was on again.
>
> Removed the alternator and battery and had them tested at the local
> parts store. Both test good.
>
> Rechecked everything, I see on the wiring diagram there are a couple of
> wires that go to the Engine Control Unit/Module, so I take the ECU out
> and clean it's connectors by taking them off and on again a few times.
> Charge light goes out again. I shut off the car and restart 3 times
> (letting it sit a few minutes between), light goes out immediately when
> engine starts as it has when things were fine.
>
> Nope, restart car about 10 minutes later and the charge light is on
> again. No wiggling of wires or tapping on anything makes it change.
>
> I even took out the ECU and resoldered all questionable solder joints
> (I've been an electronics tech for a number of years). Charge light
> still on.
>
> During one of the times when it was working, I took some readings. I
> doin't know how meaningful they are except they tell me that it is not
> a wiring problem between the alternator and the battery.
>
> The only difference between charging and not, one of the two wires
> between the ECU and alternator: normal operation, when first started it
> is about 3.6V, dropping to about 2.5V. Later starting it and the charge
> light comes on, the same line is now about 1.5V.
>
> But without knowing which way this signal goes, I don't know if the
> fault is the alternator or the ECU telling it the wrong thing.
>
> I see some mentions here of worn out brushes. Where might I find those
> in the northwest USA? I've checked a few places like Autozone and it
> lists them but says unavailable.
>
> Thanks,
> Steve
>
I'm joining the chorus for the alternator. Looking at the Helm manual, the
alternator internals are not the classic arrangement, where generated
voltage from the windings are used to self-excite the regulator and the
light is in series with the regulator supply from the ignition switch. In
those, brush failure is silent - the light doesn't go on because the
regulator doesn't draw current to feed the field through the brushes.

If the manual is right, the light is a warning light from the regulator and
comes on when the regulator can't (or doesn't believe it can) set the
alternator voltage correctly. That covers quite a bit of ground. The ECM
appears to come into play only through the "FR" lead - your guess is as good
as mine what that is, but my guess is that it is a "fault/regulator"
indication to the ECM.

You can troubleshoot in the car when the light is on with a DVM; the voltage
should be a shade under 15 volts DC (depending on just how cold it is under
the hood) and the AC voltage should be under 0.1 VDC. If the DC is above 16
volts or the AC is in the half volt range or above, the regulator or diodes
are bad respectively. If the AC is between 1/10 and 1/2 volt, you should try
it with another battery.

My advice (assuming the battery isn't at fault) is to bite the bullet and
get a new OEM alternator or at least an OEM alternator from a wrecking yard.
Whatever's wrong is very likely in the alternator and yours has given you
faithful service for more than a dozen years. You will probably need to
replace the alternator once before the car reaches the end of life (more
than once if you put in an aftermarket rebuilt!) and this looks like the
right time.

If the AC voltage is okay and you want to try brushes rather than springing
for a new alternator, you can look in the "specialty hardware" drawers at
your local Ace hardware store. They won't have the assembly, of course, but
they have a modest selection of brushes that may be adaptable. Other than
that, I dunno. I presume you can recognize critically worn brushes - when
the assembly is removed the brushes barely protrude enough to make contact.

Mike