Dan -
Thanks - your answer has helped even those who did not ask! Any clue
what would make an alternator repeatedly fry the field diodes
(rectifier)?
Bill
-----Original Message-----
From: owner-spitfires@autox.team.net
[mailto:owner-spitfires@autox.team.net] On Behalf Of DANMAS@aol.com
Sent: Wednesday, December 02, 1998 8:45 PM
To: A666K@aol.com; Spitfires@autox.team.net
Subject: Re: URGENT!!! please help
In a message dated 98-12-02 18:36:13 EST, A666K@aol.com writes:
> So when I got to where I'm now, I put a voltmeter on the batt. and
noticed
> it
> was only at 11.9, when the key would be turned to on it would drain
rapidly.
> So i disconected everything from the positive post(starter
solenoid?) and
> started plugging things back in. Nothing would cause drain except
the 2
> large
> brown wires. One wire would not drain if the alternator socket
(which
> contains brown wires) was disconnected, the other would drain no
matter
what.
>
> So now the car is dead, I am stuck and I need your help finding
what is
> shorting so I can get home.
>
> Sorry for the length and thanks in advance.
> Avi
> &Cheech my' 78 spit
> p.s. to top it all the IGN. lamp is burnt
Avi,
First of all, you need to replace the alternator warning (IGN) lamp.
Without
it, the alternator won't work.
Of all the wires on the starter solenoid (+ battery post), the only
ones you
need to worry about are the two brown ones. One of these is larger
than the
other. The smaller of the two is the voltage input to the alternator
regulator. This wire tells the alternator how much voltage there is in
the
system, so the alternator can raise or lower the output voltage as
required.
The larger wire is the main feed to the entire car - everything in the
car
receives power from this wire.
The smaller brown wire will have a small drain on it at all times from
the
regulator circuit. This is normal, but should not be more than a few
milli-
amps. The larger brown wire should not have a drain, unless something
in the
car is on.
There are three fuses in your car:
One fuse has red wires on it, and these red wires feed the
parking/marker
lamps. There should be no voltage on this fuse if the headlight switch
is off.
If you are not driving at night, you don't need this fuse.
Another fuse has green wires on it. These green wires feed all of the
accessories that operate only when the key is on, such as wipers,
brake
lights, etc. With the key off, there should be no voltage on this
fuse. The
only thing you NEED this fuse for is the turn signals and the brake
lights. If
you are careful, and use hand signals, you cas get by without this
fuse. The
ignition/coil does NOT receive power from this fuse.
The third fuse has purple wires on it, and these wires feed such
things as the
horn, hazard flasher, etc. there should be voltage on this fuse at all
times.
You can get by without this fuse.
If you have no voltage on the red wire fuse with the headlight switch
off, or
the green wire fuse with the key off, then you can eliminate anything
from
these fuses as your source of the drain. If you have voltage under
these
conditions, there is a problem with the switches. You can either fix
the
switches or pull the fuses, and test again for a drain.
Pull the purple fuse, and see what happens to the drain. If it goes
away, just
leave the fuse out till you get home and get time to fix the problem.
The large brown wire mentioned earlier goes to a four way splice, and
then to
four places:
1) To the fuse for the purple wires
2) To the ignition switch
3) To the headlight switch
4) To the alternator - this is the main charging lead from the
alternator
Any drain you are getting from the battery has to come from one of
these four
connections.
Pull the purple fuse, pull the brown wire from the igntion switch and
the
headlight switch, and remove the plug from the alternator. If you
still have a
drain, then one of the wires from the four way splice mentioned above
is
shorted to ground. If you don't have a drain, replace the wires one at
a time,
and see which one brings back the drain.
All of the above is based on the wiring diagrams I have in a Haynes
manual,
and sometimes the wiring diagrams are wrong, so you may have a
slightly
different set-up than described, but the principles are the same.
I've rambled a lot, but I figured you would rather have a ramble now
than a
thought out response tomorrow. If I'm wrong on anything, I know
someone on the
list will let us know.
Digest all of this, and see what you can come up with, and let me
know. I read
my e-mail several times a day, so I will look for your post. You are
on AOL so
you can IM me if need be. When you find the wire with the drain, we'll
go from
there.
I just went back and re-read your post, and I may have rambled on for
nothing.
You said you have the drain with the key on; I assume you don't have
it with
the key off? Is this is the case, pull the green fuse. If the drain
goes away,
the trouble is downstream of the fuse, and you can isolate it by
pulling the
green wires from various loads till the drain goes away. If the drain
is still
there, Pull the white wires from the ignition switch. Drain still
there? Pull
the rest of the ignition switch wires one-by-one, till the drain is
isolated,
and follow that wire to the short.
How large is the drain? It may be normal, and just the power to the
ignitin
coil and/or the solid state ignition system. I don't have enough
details to
know how much this would be, but on a points type, it could be as much
as 3
amps, if you just happened to stop the engine with the points closed.
Pulling
the white wires from the ignition switch will remove the coil/ignition
system
from the battery.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8
insertion - see:
http://www.sky.net/~boballen/mg/Masters/index.html
'74 MGBGT---3000mile/year driver, original condition - slated for a V8
soon
'68 MGBGT---organ donor for the '74
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