JC
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| posted on 2/10/17 at 12:07 PM |
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Fog light - what am I missing?
Hi there,
Trying to wire in the rear foglight (item 104 on the diagram). I am using the Ford Fiesta Switch, and multi plug but made a few minor changes to the
wiring - Og/Gn shown on the diagram isn't connected to the fuse as shown on the diagram, however I have 12v at it.
When I press the switch, the foglight illuminates momentarily then goes out. None of the lights in the switch light up.
I have tried 2 switches with no changes.
What am I not understanding - surely if I have 12v at both inputs all should be well??
 
Fog Light Wiring
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loggyboy
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| posted on 2/10/17 at 12:36 PM |
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Switch is probably non latching - so that when installed in the fiesta, it self cancels when the lights or ignition is switched off.
Mistral Motorsport
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ste
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| posted on 2/10/17 at 01:42 PM |
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According to that drawing it is a latching switch.
can you test the switch and see what's happening when you push it?
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loggyboy
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| posted on 2/10/17 at 01:47 PM |
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What year fiesta? As mk5 went had a GEM system so switch might not be as the diagram you are using. Is switch definitely from the year/car you expect?
Mistral Motorsport
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JC
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| posted on 2/10/17 at 02:13 PM |
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It is/was a MkIV Fiesta, with a latching switch....
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ste
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| posted on 3/10/17 at 04:55 AM |
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so if you put your tester between og and og/ye does it latch or not?
any other inputs won't make any difference to the operation of that switch in the diagram.
also, just make sure you don't have a front fog switch as the colours are the same but go to different pins.
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JC
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| posted on 3/10/17 at 06:34 AM |
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It's definitely a rear light switch - I've tried 2 as I thought it might be faulty 
When you say 'put your tester between og and og/ye' do you mean with the switch plugged in and powered, or removed from its socket?
When plugged in, when you press the switch the light comes momentarily, but the latch doesn't make. My understanding is that the switch is
like a relay -the og/gn links to earth and powers the latch, the og provides power to the lights through og/ye - is this correct?
This is really doing my head in!!!
Thanks for the patience!
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loggyboy
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| posted on 3/10/17 at 06:50 AM |
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Havr you tried with a generic on off switch?
Mistral Motorsport
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JC
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| posted on 3/10/17 at 08:27 AM |
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OK, so I set up a test circuit and got the same results. However, I found that is I put power to the 'spare' pin on the plug, the LED to
indicate the fog lights were on was made. Perhaps I have a rear switch but am connecting it to a front fog socket?
The pins are as follows:
PIN 8 X OG/GN. PIN 6 X Spare
PIN 4 X BK. PIN 2 X OG PIN 1 X OG/YE
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ste
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| posted on 3/10/17 at 02:08 PM |
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the diagram doesn't have the pin outs on it so you won't know.
the two white rectangles in the switch diagram are the switch illumination. one of them is to light up the switch when you turn on the lights and one
the fog tell-tale.
front switch uses the same colours for the switched part
ignore everything other than the two wires that actually switch, so test og > og/ye as per the rear switch with no power applied and not connected
to anything else
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JC
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| posted on 3/10/17 at 03:50 PM |
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When I press and hold the switch, the og and oy/ye make - the fog light illuminates but the tell tale in the switch doesn't.
However, the switch doesn't 'latch' in place to keep the light on
The bulb is 21W, so I make that a draw of around 1.75A - I don't think I need a relay for that - can I just wire in something like this?
Rear Fog Light Easy Push Button Switch Truck Van
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matt_claydon
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| posted on 3/10/17 at 04:34 PM |
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Have you connected the switch's ground connection? It would need that for both the illumination and latch to work if it's an electrical
latch rather than mechanical.
[Edited on 3/10/17 by matt_claydon]
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JC
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| posted on 3/10/17 at 04:39 PM |
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Hi Matt,
I have connected pin 4 to earth. This makes the internal backlight in the switch work, but doesn't help the latching......
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JC
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 posted on 5/10/17 at 06:06 PM |
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OK, gave up on the Ford Switch and bought a Hi-amp rocker switch. I now have working fog lights that only come on with dip and main beam.
For sale Ford Fiesta Fog light switch 
lol
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