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TomoHawk

Wiring a Driving Lamp Relay

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Hello!

I am installing some driving lamps, and I will use a relay.  I can wire the relay directly to a switch, but common sense (state laws) tell you that driving lamps are only supposed to come on with the high beams. 

So I have a 12V feed from the  ACC  circuit on the fuse panel to the relay, and I wanted to wire the relay's ground to the high-beam  (ground) wire  so the driving lamps come on with the high beams, because the high beam switch goes to ground, right?  Attached is a simple schematic. 

BTW- It's a 1978, so the High beam wire is a RW wire, according to the FSM

 

 I atached a simple diagram

 

 

Driving Lamp Relay.png

Edited by TomoHawk

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I'm not exactly sure how you're circuit is intended to work. Can you add the internals of the relay to the drawing? Reason I ask is that (without any details of what's inside the relay box) my assumption is that you are using a DPDT relay and switching both the hot and ground sides of the power headed out to the driving lights?

And with that assumption in mind... That will work, but is not ideal. You really only need to switch one side, and any additional contacts in the system is additional resistance that will rob brightness and add heat where you don't want it.

The way you've got it drawn, you are running both the actuation current for the relay and the current that powers the lamps through the switches and the relay. Kinda defeats the purpose of using a relay in the first place. The real reason to run a relay is to isolate the high current load side from the low current signal actuation side.

And if my assumption about using a DPDT relay is NOT correct, and you are actually planning to use a single pole relay (SPST), then what you have drawn will not work.

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On 4/13/2018 at 4:10 PM, TomoHawk said:

 

 but common sense (state laws) tell you that driving lamps are only supposed to come on with the high beams. 

 

 

 

 

Where do you get that? My Fusion and Sonota are not wired like that from the Factory.

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That's how it is in PA. Fog lights are only allowed to be on with the low beams, and driving lights are only allowed to be on with the high beams. At least that's how it was the last time I read the inspection regs that carefully.

Of course, the day and age of people adding fog lamps and driving lights to their cars seems to be mostly a thing of the past. Years ago, all the cool kids did it. But today, the only aftermarket lights you see on anything are pick-em-ups.

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Asian brands don't seem to care about American regs.  They just want to "make people happy" to sell more cars and thus give them millions of watts of light to light the road and everything to both sides.  That makes Americanians think it's OK to drive with fog lights on always or when it's not permitted.  I tell people it's ILLEGAL in Ohio, and they say they use fog lights for "safer driving" or they have bnad eyes add "need more light."     SUVs and big pickups are worse- the lamps are at eye-level.

Bruce-

I'm sorry; I forgot the put the chassis ground for the lamps.  The relay is SPST and only switches the hot, and the relay gets its supply directly from the battery;  the small switch is a toggle to enable the relay.  This diagram should be correct.

Driving Lamp Relay.png

Edited by TomoHawk

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9 hours ago, Lumens said:

My Fusion and Sonata are not wired like that from the Factory.

Then you are probably in violation of the regs in many, if not most, states.  You should take the vehicles to the dealer for immediate corrections, or you need to read the owner's book, and your state's motor vehicle regulations, to  find out how to properly operate the lights.

Edited by TomoHawk

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A problem I discovered was that the RW wire to the turn signal lever/beam switch  is grounded regardless of whether you toggle it. 

 

Headlamp circuit.png

Edited by TomoHawk

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Yeah, that could be a problem. As drawn, it is entirely possible that resistance(s) of the filaments is so low that they may pass enough current to actuate your relay sometimes when you don't want it to actuate. Namely, when the headlights are off.
 
When the headlights are turned on, what you have drawn will work fine.  But when the headlights are turned OFF and your driving light switch is turned ON, you may pull enough relay current through the headlight filaments to actuate your relay. I don't think it would be enough current to be visible in the form of even a dim glow at the headlights, but it would probably be enough to close your relay.
 
The way to combat that would be to connect the high side of your actuation switch to the switched headlight power instead of directly to the battery. If you connected the right side (as drawn in your sketch) of your driving light switch to either the Red or Red/Yellow (either one will work) wires heading out to the headlights, then that will take care of that issue.
 
Or you could use it as a "feature" to be able to turn the driving lights on without the headlights. Even though it's not the way things are supposed to work.

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The relay enable switch is connected to accessory circuit- the defog switch.  Regardless of whether the switch is on, the lights are off when you turn off the keyswitch.  Before, I used de FOG switch  to turn on fog lamps, so I'm just rewiring the relay for driving lamps, which should only need the one minor change.

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