Hi Kendall,
I just rebuilt a "5-wire" 17ACR alternator to replace the alternator on my
74 TR6 (I got some parts off eBay cheap). The original 18ACR alternator I
took out has the same connections your describe. I noticed the IGN light
was glowing at night, which I think is a bad diode.
Anyway, the separate small brown wire connects to the regulator to provide
a battery reference voltage. Later 18ACR units apparently used regulators
that didn't need that connection as it done internally. (see page 494 in
the Bentley TR6 manual). According to the diagram, the regulator connects
that to ground through 2 resistors (and decides how much to charge the
battery, I guess). I measured the resistance from that connection on my
18ACR alternator and got about 3000 ohms. This works out to .004 amps or
.05 watts, so there is some drain on the battery. But it's about the same
as a digital clock and nowhere near the 4 watts you got.
I don't know any more about alternator working than what I learned putting
the other one together (which took 2 tries) so hopefully someone with real
knowledge will help. I'd say the regulator is faulty if the current flow is
through the small brown wire. What is the resistance to ground through that
post on the alternator?
Jeff
CF13816U
----- Original Message -----
From: "Kendall Larsen" Sent: Sunday, August 21, 2005 11:34 AM
Subject: Trickle Discharger
> Hey Team,
>
> I'm trying to track down an electrical gremlin, maybe one of you can help
> me
> out. The battery goes dead on my 1974 1/2 TR6 if I don't drive it
> everyday.
>
> I measured the current at the negative battery post with the ignition
> switch
> off and I saw 320mA. (That's 4 Watts yikes!)
>
> Ok, so the current is flowing somewhere, I pulled all the fuses at the
> fuse
> block and still saw 320mA of current flowing with the key off. Took a look
> at
> whats connected directly to the battery, looks like starter, headlights
> switch,
> and alternator.
>
> I disconnected the alternator plugs. And the current draw with the key off
> dropped to 6mA. I reconnected the plug with the large brown wire and the
> small
> brown/yellow. And the current bumped up to 9mA. There is another brown
> wire
> that is smaller that has it's own connection -- when I connect this
> smaller
> brown wire by itself the current jumps back up to around 290mA!
>
> When the key is turned to the "on" position the "IGN" light glows
> brightly.
> When the car starts up, the light goes out as expected. Running voltage is
> 14.0V
>
> Is this smaller wire that goes into the alternator by itself the "sensing"
> input for the regulator? Possibly a damaged regulator in the alt?
> Everything
> seems to be running normally, except for the discharge current with the
> battery
> off.
>
> I left my headlights on all day at work recently, and had to jump start
> the car
> to get home. Maybe I messed something up recharging the dead battery from
> the
> alternator?
>
> Any other tests to suggest?
>
> Kendall
> San Clemente, CA
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