electrical puzzle - ROW 110 - Defender Source
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  #1  
Old November 12th, 2014, 04:43 PM
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Jack
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electrical puzzle - ROW 110

If you are interested in helping others (like me) to understand automotive electrical systems please read on and offer your ideas. The following description might sound confusing but I will do my best.

Started '88 110 the other morning - no heater fan
checked fuse - OK
went to fan motor, disconnected 3-way plug from wire harness at the fan motor(comes from dash)
Used separate car battery and tester leads - confirmed fan ran fine, positive to purple wire and then high and low speed depending on which green wire I connected to the negative battery terminal.
So fan motor is fine.
Fan speed control appears to be controlled inside the fan housing, like other vehicles probably some coils in there with different resistance.
Observing 3-way wires on motor side of plug I see purple goes straight to fan motor and two greens go into fan housing (resistors).
So I abandon the original fan speed switch on the dash, buy a new on-off-on toggle switch at NAPA (its winter need a fix and now)
I provide fused (10A) 12V+wire from battery to purple wire (goes straight into fan motor) then bring a new chassis ground to the center terminal (off position) on the on-off-on switch. Then I bring a wire from each of the two "on" terminals to the two green wires on the three-way plug at the fan motor. The idea is that the two "on" positions on the 3-way switch offer different paths to ground - going through the resistors in the fan housing and provide the two fan speeds.

It works perfect - all is good. I have high, low and off.

So at this point the 3-wire harness that comes from the original switch (two green wires) and the fuse box (one purple wire) are no longer connected to the fan motor in any way PLUS I pulled the 10 Amp fuse for the fan from the fuse box

The only wires going to my fan motor come from a new fused 12v supply from battery and the two wires from the new on-off-on switch.

Then today (for grins I guess) with the fan running on high (using 3-way toggle switch) I decide to move the original fan lever control on the dash and damn if the fan doesn't go into hyper drive - the original fan switch is somehow affecting the fan speed even though it is no longer connected to the fan and even though the fuse for the original circuit has been removed. If I turn the fan off using the new on-off-on switch it goes off. In other words the old switch only seems to have any effect is when the 3-way on-off-on switch is also on.

I suspect (its always the freakin' ground in Land Rovers!!) that somehow the original switch is offering a better path to ground and the fan speed is respongding like it has an uncontrolled 12v power supply when both switches are on high setting.

but HOW can this be with the wiring from the original switch no longer connected to the fan motor in any way?

If this intrigues anyone I'd love to hear your thoughts.
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  #2  
Old November 12th, 2014, 05:24 PM
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Robert Dassler
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I believe that the fan speed switch also has a control cable attached to it that controls airflow through the system. When you move the original fan speed switch to high, you are also opening a flap in the heating system allowing for increased airflow. The fan probably isn't working any better, you are just letting more air through and hearing more noise.
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  #3  
Old November 12th, 2014, 05:40 PM
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Thanks Rob

Thanks Rob - that would make sense and explain what I am hearing and seeing -
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  #4  
Old November 12th, 2014, 06:54 PM
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Robert Davis
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I believe that Robert has gotten the levers confused.
On your RHD 110, the lever on the right of the gauges open the flaps which is completely separate from the electrical switch on the left of the gauges.

You need to study the wiring diagram because it's impossible for me to tell where you tapped into the loom which is always a very very very bad idea.

For some crazy reason on some of the late Series IIIs going up into the 110s, the fan runs off an orange and brown wire (if my memory is correct) that has a separate under dash fuse which is silly, but it is what it is.
This may or may not be true of your ride, but am also suspicious of the way your fan was wired to begin with... again a proper diagram will show the wiring.

Purple is generally (+) fused. Green is generally (+) fused when the key is switched on.
I suspect you had corrosion on your bullet connectors or the fan switch which is actually a rheostat that varies power output, was somehow bent away from the coil and not making contact when it wasn't working a very common problem from people getting heavy handed on the switch lever.
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  #5  
Old November 12th, 2014, 07:16 PM
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shayne young
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Levers on the left are directional and heat only..I believe the fan speed lever does indeed open a flap allowing air into the vehicle..this allows you to stop air from coming in all the time.. The first half of the travel of the lever opens the flap and then the second half of the travel is the fan speeds..this allows you to have fresh air flowing in without the fans on..should you desire..
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  #6  
Old November 12th, 2014, 07:21 PM
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will check

Thanks again,

I did study the wiring diagram on my 110 CD and the wire colors in my 110 coincide with the drawing so I think we are OK their. The illustration on my fuse box cover shows the fan symbol as a 10A fuse located 3rd location from bottom - left side.

Easy enough to have a look behind the binnacle tonight and look at the original switch wiring and also to see if there is in fact a cable hooked up to the original electric switch.

Like you I thought the only real cables were both on the other side - one to control the temperature and one to direct air between the heater and defrost.

Also just to be clear - I did not tap into the loom (strictly speaking). I just pulled apart a multi-plug connector (separating the fan motor from the loom, at the motor) and provided an alternate power supply and switching into the multi-plug. Makes it simple to reassemble if I find a more professional fix.
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  #7  
Old November 13th, 2014, 08:12 AM
the rover shop
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shayne young
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The cable from the switch is the one on the inside edge of the vertical surface... Close to the firewall...when you move the lever you can feel it operating a cable before you hear the clicks of the fan speed... Not to second guess myself but I checked on a row truck I have here..)
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