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Sahara

Fog and driving light wiring options

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So my '02 came with Hella 500's that worked fine until the switch in the dash (they were wired to the factory front fog light switch) failed. Further, the shop said they weren't really wired right and a rewire would be called for if they were to be reliable, and the bad wiring was likely what blew out the OEM switch. They showed me the wiring and I agreed, it was a hack job, likely done by a previous owner with limited expertise. My current plan is to have the Hella 500's wired up properly and add fog lights on the underside of the bumper, as shown in the attached picture of somebody else's lovely 2002. The biggest challenge I can foresee is that the battery is in the trunk, making connecting the lights to the battery a bit tricky, if that is called for, which I believe it is. The car was reupholstered after the battery was moved to the trunk so all the wiring involved was nicely hidden and I don't want the upholstery to be cut into, especially by the shop I plan to use, which specializes in off-road lighting for trucks, mostly, and not in anything to do with classic cars. I also want to put the lights on their own switches that ARE NOT related to any of the switches BMW included in the car, so that I don't have to worry about replacing/rebuilding the old BMW switch gear. I'm sure there are plenty of you that have aftermarket driving/fog light setups and batteries in the trunk. I'd be interested to know how you wired that up and what was required? 

post-42945-0-40288700-1375305299.jpg

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It sounds like it was wired up without the benefit of a relay to switch the relatively high current of the lamps. Instead you would have had the feed for the lamps running from under the hood to the dash switch and back. This was indeed a hack job. 

 

Your power under the hood can be taken from the large terminal on the starter motor. This will be connected to the battery so you won’t need to upset your upholstery to get at the battery again. This should be wired directly to a fuse. This can either be an in-line arrangement or even a fuse box with multiple fuses. Given your plans for multiple sets of lights a fuse box may be better. 

 

From your fuse you would then run to a new relay, generally located above where your battery used to be. This is then run from the relay to your lamps. This way the higher current wiring is limited to between your starter motor and your lights. Much more direct. 

 

The relay is then wired to be energised by what ever switch you switch you want to control your lights with. This has a separate feed that you can pick up from any connection under or around your dash that’s switched by the ignition. This feed runs, via your dash switch to the relay under your hood (follow the path of the wiring running through the firewall grommet on the left side of the firewall under the dash. This can then follow the loom to where the relays are. The other side of the relay control coil is then connected to ground. 

 

Search on this site site for a wiring diagram, there is a great one that shows all of this together and is based upon operating the lights with the high beam and an auxiliary switch. 

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2 minutes ago, Simeon said:

It sounds like it was wired up without the benefit of a relay to switch the relatively high current of the lamps. Instead you would have had the feed for the lamps running from under the hood to the dash switch and back. This was indeed a hack job. 

 

Your power under the hood can be taken from the large terminal on the starter motor. This will be connected to the battery so you won’t need to upset your upholstery to get at the battery again. This should be wired directly to a fuse. This can either be an in-line arrangement or even a fuse box with multiple fuses. Given your plans for multiple sets of lights a fuse box may be better. 

 

From your fuse you would then run to a new relay, generally located above where your battery used to be. This is then run from the relay to your lamps. This way the higher current wiring is limited to between your starter motor and your lights. Much more direct. 

 

The relay is then wired to be energised by what ever switch you switch you want to control your lights with. This has a separate feed that you can pick up from any connection under or around your dash that’s switched by the ignition. This feed runs, via your dash switch to the relay under your hood (follow the path of the wiring running through the firewall grommet on the left side of the firewall under the dash. This can then follow the loom to where the relays are. The other side of the relay control coil is then connected to ground. 

 

Search on this site site for a wiring diagram, there is a great one that shows all of this together and is based upon operating the lights with the high beam and an auxiliary switch. 

This is great advice Simeon but I will note there is a relay, and a functional one as it was tested by the shop, between the lights and the switch inside. 

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2 minutes ago, Sahara said:

This is great advice Simeon but I will note there is a relay, and a functional one as it was tested by the shop, between the lights and the switch inside. 

 

Ahh. I wonder why it burnt out the switch then?

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Just now, Simeon said:

 

Ahh. I wonder why it burnt out the switch then?

I was told that some element of the crappy current wiring was connected to the distributor and taking power from there somehow. Unless they confused the starter for the distributor then that certainly sounds like an issue. Further, I did start and stop the engine with the driving lights switched on quite a few times which, whether the distributor or starter or both were involved could have sent some sort of spike through the system. 

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Switches fail over time, even in a properly designed circuit with a relay to buffer the switch. Hard to say without seeing a diagram of your circuit if or why starting the car with the switch on would stress the circuit. Seems unlikely.

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(edited)
2 minutes ago, Chris_B said:

Switches fail over time, even in a properly designed circuit with a relay to buffer the switch. Hard to say without seeing a diagram of your circuit if or why starting the car with the switch on would stress the circuit. Seems unlikely.

Fair enough. I’m a pilot and I’ve always been taught, in planes, to shut down all the avionics before killing the engine to avoid damaging them, I figured something similar was possible in older cars as well. 

Edited by Sahara

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Generally good advise, although modern cars are designed to avoid these problems. Avionics no doubt use complex electronics, whereas an automotive fog/driving light circuit doesn’t. The switches (both in the relay and on/off button) are essentially mechanical and stout. The relay is the most complex part and is designed to take a beating. A typical lightning relay should be rated at 30-40 amps. Even if you are running 100 watt bulbs (x2) that would be less than 20 amps, a more than reasonable safety margin. 

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The approach I took for the driving lights was to tap power to energize their relay off the out from the high beam relay; this way the driving lights only work with the highs, and are automatically switched on or off with them, provided their dedicated interior switch is on. You do the same for the fogs with the low beams if you wish, though this eliminates the possibility of use the fog lights exclusively. There are unused connections in the fuse box that you can tap for primary power, or you can pull directly off the starter and use a modern relay with an integral blade fuse. No reason to go all the way back to the trunk for the battery.

 

Work out a plan of exactly how you want the lights to function, then use that to figure out the wiring. Relay everything.

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Read my article that @Simeon linked to in the fourth post (thanks Simeon!) and wire your lights and 500s up that way.  Then you can add another relay (controlled by the fog light switch) to run the lower fogs. The advantages of my method include:

 - Daytime running lights

 - No high current from bulb loads going through the factory interior switches

 - Proper relay control for all lights

 - Proper DRL/low/high/driving beam usage automatically with just the original switches (lows go off when highs come on, etc.)

 - No cutting of factory wiring harness

 - Only need +12V battery power, ground and switched light signals (all readily available up in the front drivers side of the engine bay)

If you need more relay real estate, put in one of these relay boxes:

https://www.amazon.com/d/Starter-Relays/ONLINE-LED-STORE-12-Slot-Installation/B072KJNPHJ

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Jumping on this excellent thread as I contemplate installing driving lights.  Still absorbing learning regarding wiring, and especially like AustrianVespaGuy’s diagrams for daytime running lights with a nighttime driving light option — ie, ability to run with or without the driving lights when in high beam, depending on main driving light switch setting.  For purposes of my main driving light switch setting, I have the coveted green fog light switch, provided by Ray - who wants it back if I don’t promptly put it to use!  See photo.

 

So I am seeking any available learning about how this switch normally would be wired to run fog lights, what each pin is intended to connect to, etc.  I don’t find this switch in my tii wiring diagram, but note that it is lit by applying 12v to “center” pin.  All the other pins have continuity when the switch is on.  I figfure I should ground one pin, and run another to a fresh high beam power relay. Where does the third one go? And to what does one connect the center pin (green-white “switched/fused” power)?  

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43 minutes ago, 0257 said:

So I am seeking any available learning about how this switch normally would be wired to run fog lights

 

Your green round workable fog light switch is a nice find!  

I used a lighted pull switch for my fog lights...3 pins (one is ground).

Here's the wiring diagram I used:

 

Fog Light Wiring.jpg

 

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Thanks, John.  This will be helpful.  And further digging on the faq reveals a pretty direct answer, from SteveJ, to my “what do the pins do” question.  The project is underway. K2CC6C370-3E3B-4B27-A860-8A87F248537B.png

 

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