Would this make a good rear fog light?

toledoUPSguy

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Night shot.
 

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toledoUPSguy

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Any chance you might run it for 20 minutes or so and get a lens temp reading, compared to ambient?
ran it for about 25 minutes when I got home sitting inside the cab of my truck. Could not feel any temp difference at all and I don't have access to the temp gun any more. Sorry can't be more helpful.
 

toledoUPSguy

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That is just about a textbook example of a correct rear fog installation. Nic work!
Thank you. It was a lot of work, especially trying to get the wires into the cabin. Unfortunately I'm not done, have some trouble shooting to do. Works perfectly when acc power is on, shuts off almost instantly as soon as you start the engine.
 

toledoUPSguy

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Thought it might be a bad ground connection so I redid it, no change. I can shake all the connections in the harness and it doesn't shut off when the engine is off so I'm guessing all my junctions are good. I'm really at a loss with this. Probably a stupid question but is it a problem to have the relay upside down?
 

Alaric Darconville

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Probably a stupid question but is it a problem to have the relay upside down?
Does the relay flip upside down when the engine is running?
Seriously, though-- does it come back on when you press the switch again? It's probably something to do with the the way many things on the ACC circuit shut off temporarily when you crank the engine.
 

toledoUPSguy

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Does the relay flip upside down when the engine is running?
Seriously, though-- does it come back on when you press the switch again? It's probably something to do with the the way many things on the ACC circuit shut off temporarily when you crank the engine.
This is a momentary switch with a latching relay. It is working as designed until I start the truck. Power to the relay is one of the front fog lights. This way the rear can never be on if the front isn't. So when I go from vehicle powered but engine not on all is well. When I go to start the engine the rear fog light goes out as designed because the front fogs turn off while starting. Pushing the rear fog light button again doss not turn the light on and if you hold the button the relay buzzes. Shut the engine off and turn the truck back on with engine off, hit button and rear fog back on.
 

Alaric Darconville

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This is a momentary switch with a latching relay. It is working as designed until I start the truck. Power to the relay is one of the front fog lights.
You might think this is a good idea, but there are so many conditions where the rear fog lamp is warranted but the front ones are not. The biggest example is extreme rain or fog in the daytime. In the daytime, you're not really going to see much better with them yourself but the direct and *specular* glare from them will affect oncoming drivers. Even at night, the rear fog lamp is useful at a higher speed than front fog lamps, since you only need the front ones if the lower atmospheric disturbance is so severe you have trouble seeing the road markings.

Maybe you should pick a different "hot when ACC/ON" source. Other lighting circuits may also have some complexity to them, but using the low beam instead of front fog lamp circuit might be better.
 

toledoUPSguy

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I am try to wire them up like they would come from the factory. Rear fogs according to the ECE regulations cannot be switched on without the front fog lights being on.
 

Alaric Darconville

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I am try to wire them up like they would come from the factory. Rear fogs according to the ECE regulations cannot be switched on without the front fog lights being on.
There's an "or" in there:
Addendum 47 R48
6.11.7. Electrical connections
These shall be such that:
6.11.7.1. The rear fog-lamp(s) cannot be switched on unless the main beams, dipped-
beams or front fog-lamps are lit;
(I don't recommend them being allowed to be on when the high (main) beams are on, though).

The reason for the "or" is that in the ECE, rear fog lamps are required equipment but front fog lamps are only *regulated*, so that means there may be plenty of cars with a rear fog lamp but no front ones.

Front fog lamps generally have various interlocks on them, such as the one that shuts them off temporarily when you go to high beams (and then they usually restore themselves when you return to low beam). It's possible such an interlock is contributing to your unusual issue.
 

-Virgil-

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Buzzing relay sounds like a PWM (pulse width modulated) feed to the front fog lamps, which could mess with your rear fog switch/relay setup (no, relays don't care which way is up). You should be able to work around this by putting a capacitor across the coil pins (85 and 86) of the rear fog relay, and a diode in the wire connected to the rear fog relay's 86 pin, all as per this sketch.
 

toledoUPSguy

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There's an "or" in there:

(I don't recommend them being allowed to be on when the high (main) beams are on, though).

The reason for the "or" is that in the ECE, rear fog lamps are required equipment but front fog lamps are only *regulated*, so that means there may be plenty of cars with a rear fog lamp but no front ones.

Front fog lamps generally have various interlocks on them, such as the one that shuts them off temporarily when you go to high beams (and then they usually restore themselves when you return to low beam). It's possible such an interlock is contributing to your unusual issue.
thank you for that, the OR does indeed make a difference. I already have a headlight harness splitter that has unused taps for the parking lights. May try that later.
Buzzing relay sounds like a PWM (pulse width modulated) feed to the front fog lamps, which could mess with your rear fog switch/relay setup (no, relays don't care which way is up). You should be able to work around this by putting a capacitor across the coil pins (85 and 86) of the rear fog relay, and a diode in the wire connected to the rear fog relay's 86 pin, all as per this sketch.
Always appreciate your help. If this was the case wouldn't it also be causing a problem when the whole vehicle is powered up without the engine running?

I'm thinking I might have a ground issue (although in my simple mind it would show up with engine off) I have all the grounds tied to the negative of the front fog light. I probably should try grounding the rear fog and relay to the frame.

Might have to wait till tomorrow since my body freaking hurts from all the crawling around, kneeling and laying on my back yesterday. Getting old sucks.
 

toledoUPSguy

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For a quick and dirty check I changed the supply power to the relay to a cigarette lighter plug. Works as it's supposed to. Now the real question is will the parking light circuit going to be any better since all the lights on the truck are BCM controlled LEDs?

Crap crap crap.
 

-Virgil-

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Crap, what? I told you how to make your rear fog relay get along with your PWM light circuits...
 

Alaric Darconville

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thank you for that, the OR does indeed make a difference. I already have a headlight harness splitter that has unused taps for the parking lights. May try that later.
(regarding PWM) Always appreciate your help. If this was the case wouldn't it also be causing a problem when the whole vehicle is powered up without the engine running?
PWM may only occur when the alternator is delivering power (or when the key is on). I feel a little dumb by not suggesting that it could be a PWM issue myself. It was in my brain but didn't make it to my fingers so -Virgil- beat me to that punch.
 
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