Defroster Switch Wiring

[rick3000]

Particlewave, I need your wisdom!



This is the wiring diagram I used when I wired this modification. I just hooked up the illumination wiring and the fan switch is always illuminated (backlit). When I turn the headlights on the switch backlight changes to my set backlight brightness (set by the knob on the instrument cluster), however the backlight is operating inversely to everything else. If I raise the brightness the switch gets dimmer, if I decrease the brightness the switch gets brighter.

If I swap out the 12V from the phone connector (Switch Pin 4) with the Illumination+ and put Illumination- on Pin 3, the backlight works properly but since the latching relay requires 12V the switch only works with the headlights on.

When I try the Illumination- on Pin 3 instead of the Illumination+, the switch is still always illuminated, but I lose any brightness adjustment.

I have tried every configuration I can think of and am completely stumped as to why the switch is acting like this. I believe it "should" work, but it doesn't. I would greatly appreciate any insight, because I have been racking my brain for the last several hours.


The only solution I have come up with that actually works (switch only illuminated when headlights are on and brightness adjusts properly) is to insert a 4 Pin Relay, like this, but I don't really know why this is any better. Thank you!