Fog Light Wiring Options

[b622r]

I am looking at different ways to add fog lights and looking at the wiring diagrams, I can't make sense of using the factory relay. From what I see, power runs from the PDC fog light fuse to the MFS at the column and runs power back to the relay in the PDC. This is not the trigger current but the actual power source. The relay output is 87a which is always closed. So really the relay is a passthrough. The trigger is connected to the high beam circuit so when high beam is applied it triggers the relay to route current to 87 which goes nowhere. That's how the high beams turn off the fogs. But as the diagram shows you are running full load current through the switch. Not really expandable to higher current loads as it all flows through switch.

An idea would be to rewire the fog relay so that the switched power goes to 86 the trigger, the high beam trigger is disconnected, a new power run directly from PDC fuse goes to 30 and output light blue is connected to 87...then it would function like a relay. I have spare PDC so I might play with cracking it open but running an external relay sure would be a lot easier. I could still run current through the loop to get the dash fog light indicator to light up.

Anybody else run across this?

 

[b622r]

So pretty much concluded from diagrams and reading other posts that the factory fog light doesn't use a relay. Rewiring the flog light circuit is not really ideal because it looks like 16Ga wiring/20A max. A better option if I want to leverage PDC may be the rear defogger. It's 40A circuit fuse #2 and has a 14 Ga power wire. I can grab the hot out from the HBL relay which is also 14GA and run trigger from dash switch. I could also lower the jcase fuse to 20A or 30A just to add protection knowing that my load on the circuit with LED's is probably going to be around 10amps...but I get all that extra wire capacity. Leveraging an existing circuit makes the PDC surgery more simple. I am thinking this through as I type...I have a softtop only.

 

[TheBoogieman]

I missed your question.

 

[b622r]

I missed your question.

Sorry - think as I write...multiple choice question. Does this sound like a good idea?

1. No, you will burn your Jeep.
2. Yes, but it is overkill.
3. Neutral, proceed and let us know how it works out.

 

[b622r]

Plan is coming together. I am using my existing defogger relay socket and adding another one from my cannibalized PDC. Two dash fog light switches (SW). The power side of relays will come from the 40A #2 fuse.

 

[C.J. Roberts]

I believe that you're overthinking it. All the factory wiring is in your Jeep. All you need to do, if I'm not mistaken, is to insert relays into the proper spaces in your existing PDC, free the pigtails from their stowed positions on the frame, and connect up some lights.
There's even a hack to make it so that the fog lights do not turn off when you activate the high beams. The only other thing you might need is a MFS with the fog light switch in it.
Or failing all that, run a seperate harness. Most lights can be purchased as a set with a harness that will work.

 

[b622r]

I wanted it to be expandable for future. I completed the cable runs to PDC today:

PDC donor socket ready.
System should be able to support 400watts no problem.

 

[b622r]

PDC surgery went well today. Very tight space to work but I wanted to avoid taking terminals out and breaking the tiny retaining clips

Here is PDC with relay socket from donor and two new relays.

Power from #2 fuse powering the power in (30) of relays.

 

[b622r]

 

[b622r]

Can anyone explain why this worked?

I wanted the fog instrument cluster light to come on. When either or both circuits were on. I tapped the line i ran for each circuit relay trigger and put a diode inline then connected both leads together and tapped into the WT/OR wire from the multi function switch. So the theory was that it would just energize the circuit the factory fogs use and the light would come on as described in other threads here. The diodes are to keep from back feeding current into the other switch if only one circuit was on.

At first it did not work, so I plugged the old fog light relay in and it worked. After the PDC surgery, the old fog light relay only had ground on the trigger side, the WT/OR from multiswitch on the load, and the high beam RD/OR on the trigger side. I had cut the LB load out wire because it went nowhere and I did not want a stray hot out there. So it works great but I don't know why plugging the relay back in did anything. The LB out goes nowhere because my jeep did not have factory fogs.

And there is more, once the indicator light was working, it would go off if the high beams where activated. This means the relay was breaking the connection between WT/OR and LB. This of course doesn't affect my lights because they are wired through different relays. LB on multi tester shows no ground or anything.

So I cut the relay connection to RD/OR. So now it works exactly as planned, instument lights on when either fog light circuit is powered and stays lit when high beams are on, but I don't how the relay is making the instrument light work.

 

[b622r]

Just answered my own questions...the LB out of the fog relay splits and runs back to instrument cluster and lights indicator. The relay if activated would break that circuit...which answer my first question, you have to have a connection from WT/OR to LB for indicator light to work, I actually could have made the connection from my new switches directly to LB at the PDC...may consider later but this will work for now.