> From:    Todd Last <rubatoguy@COMCAST.NET>
> Date:    Thu, 24 May 2007 19:45:50 +0000
>
> Just wondering if any of the electronics whizes out there

I don't know if I'm an electronics whiz, but I almost peed on an
electric fence once... does that count?

> could some up with a way to (e.g. wiring diagrams) :
>
> 1.) Make an indicatorl light which showed when the radiator fan
>     was operating.  Bonus points for showing which speed it is
>     running at.

There's more than one way to do it...

1) Add a wire to the high and low speed circuits at the fan motor
    connector.  Run each wire back to a couple of lights on the dash.
    This tells you that voltage is at least making it to that connector.
    It does add connections and voltage drop, which might not be what
    you want in the fan circuit.

2) Add a wire to the 2nd stage relay coil circuit at the fuse box.  Run
    it to a light on the dash.  This one won't come on until the second
    stage (high speed) kicks in, but it should have very little effect on
    the voltage drop in the circuit.  It won't tell you if the relay
    coil has failed open, or if the fan motor has burned out, though.

3) Measure the voltage drop across the fuse or across (part of?) the
    wire from the fuse box to the thermoswitch.  This will be zero with
    the fan not running, non-zero with the first stage running, and a
    higher non-zero voltage with the second stage running.  The voltage
    drop won't be enough to drive a lamp or LED directly; you'd have to
    build a little amplifier circuit to do that.  Again, very little
    effect on the voltage drop in the circuit, but only tells you that
    the fan motor is drawing current - not that the fan blades are
    turning.

4) As #3, but use a Hall-effect current sensor around or next to one of
    the wires.  Same idea, but looking for magnetic field instead of
    voltage drop.  You'd still need an amplifier and the other features
    and drawbacks of #3 apply.

5) Put some kind of tachometer on the fan blades directly.  This could
    be a magnet on one or more of the blades (with corresponding weight
    on the other side so as not to cause an imbalance), with a reed
    switch or sensor mounted near the edge of the blades.  Again, you'd
    need an amplifier to turn the contact closures into something that
    would drive a lamp or LED.  This way won't cause any voltage drop at
    all, and tells you what you really want to know - are the fan blades
    turning?  But it's also fairly complicated to set up, mechanically.

> 2.) Make an indicator light that showed when the A/C compressor was
>     engaged.

Most of the above ideas also apply.  The direct-wire idea might be a
little more practical here, but then you have to run another wire from
back to front.

Yes, I've already been told that I have too much time on my hands.  :)

Matt Roberds