Rear fog lamp switch not working?

D

doktormane

TJ Enthusiast
Joined
Jun 5, 2019
Messages
234
Location
UK
Alright guys so I am back with another issue. I am trying to install a rear fog lamp on my Canadian spec 03 Rubicon, without which I can't pass the inspection here in the UK. I got myself a factory EU Rear fog lamp switch (on euro TJs it is the same style switch as the rear window defroster switch, rear wiper and o/d switch if applicable). I also bought an automotive relay. I applied power to pin 2 on the switch and I hooked up pin 3 from the same comnector to pin 86 on the relay. I then applied power to pin 30 on the relay and used pin 87 to hook up the rear fog lamp. It didn't work. The fog lamp works, as I tested it separately. If you put power through pins 2 and 3 on the switch the little orange led will light up but only if you keep the button pressed and it turns off the moment you take your finger off. What Is the problem? I know for a fact that EU Jeeps use a weird green so called "Smart relay" for the rear fog lamp and I don't understand how it's supposed to work. I think either the switch only works together with the green relay... Can somebody shed some light on the matter and explain how the factory wiring is supposed to work? Why are pins 5 and 2 on the factory relay both getting power? Why is pin 3 on the switch connected to pin 4 on the smart relay and both connected to the lamp on the factory wiring?

Thank you in advance!

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Pin 5 is supplying power from the battery for the relay.
Pin 1 is supplying power from the battery for the rear fog itself.
The fog switch will ground the relay, when on, energizing the relay.
Pin 4 & 3 combo provide power actually to the rear fog and the indicator light in the switch.
And, of course, ground is ground.
 
I think what makes it a "smart" relay is that if your headlights are not on, the rear fog will not be on.


So...
Pins 5 and 1 on the relay in the schematic will go to pins 30 and 85 on your new relay.
Pin 2 on the jeep relay goes to pin 86 on the new relay.
Pin 4 on the jeep relay should go to pin 87 on the new relay.
Pin 3 on the jeep relay should not be needed.
 
Last edited:
dbbd1 said:
Pin 5 is supplying power from the battery for the relay.
Pin 1 is supplying power from the battery for the rear fog itself.
The fog switch will ground the relay, when on, energizing the relay.
Pin 4 & 3 combo provide power actually to the rear fog and the indicator light in the switch.
And, of course, ground is ground.
Click to expand...
But isn't the relay already ground by PIN 3 on the relay itself?

When I tried connecting the switch with a normal relay, whenever I pressed the switch the lights in the Jeep would dim a bit. What could that point to?
 
doktormane said:
But isn't the relay already ground by PIN 3 on the relay itself?

When I tried connecting the switch with a normal relay, whenever I pressed the switch the lights in the Jeep would dim a bit. What could that point to?
Click to expand...
Yes, but- it's tied into the door fuse, number 4. You know, the one you pull if you take your doors off but don't want the dome lights all of the time. Which is weird. The only thing that I can figure is that there is some little circuitry in that smart relay for "something." The way I wrote it up and the way I see it, the fog switch does the actual grounding for the lighting.
 
It's possible that the fog switch grounds the relay "only" and then the relay uses the pin 3 ground to ground the rest of the circuit, but both wires, at least after the fog switch, are 20 gauge thick (actually, at splice 207, it goes to 16 gauge but it's still 20 right after the switch). So, does it matter???
 
dbbd1 said:
Yes, but- it's tied into the door fuse, number 4. You know, the one you pull if you take your doors off but don't want the dome lights all of the time. Which is weird. The only thing that I can figure is that there is some little circuitry in that smart relay for "something." The way I wrote it up and the way I see it, the fog switch does the actual grounding for the lighting.
Click to expand...
I couldn't find the circuit diagram for the smart relay anywhere... I am thinking as well that there is something else going on in the green relay.
 
I don't it's necessary for your application though. This should get you through inspection.

Maybe it does something weird, like flash SOS when you open the door (fuse 4), who knows?
 
You would probably have to take it apart to get any inkling of what it may do. It's "proprietary."
 
dbbd1 said:
I don't it's necessary for your application though. This should get you through inspection.

Maybe it does something weird, like flash SOS when you open the door (fuse 4), who knows?
Click to expand...
I need to have a switch that lights up when the fog lamp is on and that indicates what it is. The factory switch works great for that.
 
The stock fog switch is just a switch and will work with the connections that I wrote down. If you want to be double-double sure, increase the wire size off of pin 1 on the switch to at least 18 gauge, to help handle the current.
 
dbbd1 said:
The stock fog switch is just a switch and will work with the connections that I wrote down. If you want to be double-double sure, increase the wire size off of pin 1 on the switch to at least 18 gauge, to help handle the current.
Click to expand...
Does it matter that I took the power from the fuse box and not from the headlamp switch output?
 
doktormane said:
Does it matter that I took the power from the fuse box and not from the headlamp switch output?
Click to expand...
That would mean that your rear fog could be "on" any time. Probably won't pass inspection that way.

Unless-
You did that only for pin 30 on your new relay but still used the headlight switch output for pin 85.


What is the wattage of your rear fog light?
 
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