Which ISN'T why you'd want the resistance as high as possible. Signal
circuits are very picky on what you add to them. Just be careful and don't
go overboard (such as a customer who fried his Cluster out with too many
LED's in his cab)- $900 mistake, or Best Buy tapping into the wrong wire at
the PCM and frying out an injector control circuit and an injector - $1100
mistake.
- Bernd
-----Original Message-----
From: Jason Bleazard [mailto:dml@bleazard.net]
Sent: Sunday, February 03, 2008 10:49 AM
To: dakota-truck@dakota-truck.net
Subject: Re: DML: MDS "on" LED...
Bernd D. Ratsch wrote:
>
> Just make darn
> sure you don't ground the signal circuit - PCM goes "bye bye".
Which is exactly why you want the resistance of an added circuit to be
as HIGH as possible.
It actually depends on whether you're adding things inline to an
existing circuit, or creating a new circuit in parallel. Going inline,
you want the resistance to be as small as possible so you don't affect
the existing circuit. If you're adding a new circuit in parallel, you
want the resistance to be as large as possible.
It sounds like Steve is thinking of adding a new circuit in parallel for
his LED. That would make more sense. If it was inline, then all the
current that goes through the existing circuit would drive through the
LED, which probably isn't what he wants. Who knows how much current
goes through that line, it might be too much or too little to drive the
LED. If he tries to change the resistance to keep the LED happy then it
won't make the PCM happy.
Now, if he adds a parallel circuit for the LED it's easier. There's
currently no LED circuit there, and an open circuit (or one that doesn't
exist) is infinite resistance. It therefore pulls zero current. You
want to keep it as close to the current situation as possible. Keep the
resistance as high as possible while still illuminating the LED, which
will make sure it draws the bare minimum current that it needs.
I wonder if a low-power relay would pull even less current than an LED.
Steve, if you're feeling ambitious, that might be worth investigating.
Hook up the relay input in parallel, then use the output to drive the
LED circuit and completely avoid connecting the LED to the PCM.
If you add a new low-resistance circuit, it adds a large current draw.
Zero resistance (i.e. a "short") is what lets the magic smoke out of the
parts. Remember, V=IR.
-- Jason Bleazard http://drazaelb.blogspot.com Burlington, Ontario his: '95 Dakota Sport 4x4, 3.9 V6, 5spd, Reg. Cab, white hers: '01 Dakota Sport 4x4, 4.7 V8, Auto, Quad Cab, black
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