Printer Friendly Forum Posts - fog lamp relay wiring

Hello all, please excuse me if this has been covered. I have been searching this site for hours but can't seem to pinpoint exactly what I need. I am wiring new fog lamps. I don't need a switch as I will just leave them on when headlamps are on. I just need the fog lamps to have power when low beams are on and no power when high beams are on (low beams stay on with high beams in this vehicle). Here is what I've figured out so far:

SPDT Relay:
pin 85: +12VDC lead from high beam
pin 86: ground
pin 30: fused +12VDC 10A
pin 87: not used
pin 87a: positive lead to fog lamps

Please advise. Thanks in advance for any assistance!

As long as terminal 30 only has power when the lights are on, it will work.

Ah, this is a good point and an oversight on my part. I was going to use a fused constant +12VDC for pin 30. I could power the fog lamps on the same circuit as the low beams by running the +12VDC lead from the low beams to pin 30 in order to prevent the fog lamps from having power without the headlamps on. I'd rather have fog lamps on their own circuit. Is there a single relay that can do this or do I need an additional relay here? Thanks!

what kind of vehicle do you have?

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This information is provided only as a reference.
All circuits should be verified with a digital multi-meter prior to making any connections.

It is a 2011 Chevrolet Equinox.

The idea is correct, keep that constant 10amp feed to 30 and the switched low beam output to 86 (not 85 no difference in practice but ISO convention states that 86 is the + side and 85 the - side of the coil).
Ground to 85
Here's where you went wrong.
87 to foglights.
On a 5 pin relay 87a is normally closed (NC) and is connected (continuous with) 30 until the relay coil is triggered then 87 becomes connected (87 = NO).
87a, NOT USED
That's why a 4 pin switches and a 5 pin switches and changes over hence Single Pole Change Over or SPCO.
Sorry I was so long winded.
The way you had the relay wired the lights would have been on all the time.
Some one posting above should have known better.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I have no idea who Howie is talking about that should have known better.

Howie's way will have your fogs on along with the high beams. That will probably = a ticket.

I wouid not tax the low beam circuit with the additional current of the fogs. This will take an additional relay. Wire the additional relay as follows. 85 to ground. 86 to low beam positive wire. 30 fused at the battery. 87 of second relay to 30 of the original relay.

Craig, the way I suggested it the low beam simply triggered the relay coil. I admit I should have stated pin 30 12V+ Constant from battery or fuse box input.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

It will NOT bring the fogs on with the high beams unless they currently come on together which is not going to happen if the original factory wiring is adhered to. The fact that they are triggered from the low beam ensures they will only come on when the low beams are in operation which at least makes them legal here in the UK.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

In his initial post he stated that the lows remain on when the highs are lit.

Sorry, you're absolutely right needs to go into the wiring and look at the headlight hi and low beam relays.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

It being a brand new vehicle, I would have to bet that there is not a problem with the OEM relays.

No I didn't mean a problem but maybe they are separated in the steering column loom (i.e. NC) so take the feed from there at the hi-lo switch. I'd have to know the operational parameters.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

We've come full circle, i.e. a hold a second hold off relay to break the first relay feed when the hi beams come on.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

In fact the first post was correct and so were you! I'm the idiot for not properly reading the first post.
It's like this:
High beam to 86 Ground to 85
10amps constant to 87a
Output to 30
30 to 86 on second relay
85 to ground
10amps constant to 87 (shared with 87a wire as above
30 to fog lights.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

First relay is a hi beam interlock/lockout second powers them up.
I think. You should be waking up in about 2 hrs.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Isn't it simpler with 86 to the fog switch (powered from low beam power if that is a requirement) with 85 to the high beam (bulbs - ie, 8 of their relay)?
Then 30 from fused +12V and 87 to the fogs.

Not that I analysed this 2nd page, but the OP seems to be fogs on unless its relay is on (if power to 30, hence why 30 is (low) beam power); the relay being on with high beams.

Not a big deal, but I usually prefer 87a for things that should normally be on - as in "fail-safe" alarms or devices (solenoid fails so the 87a-device is connected to 30 - eg, an alarm).

Glad someone's cut through my rubbish here. Time for Mr. I to finish his breakfast, me to wash my lunch down with 2 x Amoxicillin and a painkiller, you to go to bed goodnight antipodean chum.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

You mean I got it right? (I really did skim....)

An oft forgotten trick...
If you want A to cut out when B is on, use B's +12V as ground for A's relay.
(Add a diode if you don't want B on and A's "control" off to turn A on.)

Thanks to all for the input! Here's what I've come up with: Two Relays. First as follows: 85 to ground, 86 to low beams positive lead, 30 to fused constant +12VDC 10A, 87 to 30 on second relay, 87a not used. Second relay as follows: 85 to ground, 86 to high beams positive lead, 30 to 87 on first relay, 87a to fog lamps positive lead, 87 not used. Lets try that on for size, any thoughts?

Spot on, sorry for the confusion, as Mr. I pointed out I didn't read the first post PROPERLY.
The bit that got me was the low beams staying on when you activate the high beams, a million years ago I had a Ford Capri , the factory lamps had either H1 or H2 bulbs.
I changed all 4 to Cibies with H4s on the outers and had to relay them to run that way, i.e. like yours it has kind of stuck in my mind ever since then (1978) that ALL cars dumped the low beams when the high beams came on, stupid of me so sorry.
Incidentally in Europe, we MUST also be equipped with (slightly towards the orange) rear fog lights. Usage rules are quite strict. Basicly fog, very heavy rain or falling snow.
In the front, i.e. normal fog lights, must be a matching pair, again restricted use but the law turns a blind eye on fronts being used for "hedge and roadside obstacle" illumination.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Howie, no apologies necessary. I'm not exactly sure as to the thinking behind General Motors' engineering of the lows and highs being on at the same time. All of my current vehicles made by GM are this way. I probably should integrate a switch for the fogs but I usually leave them always on in my other car so I figured I'd do the same in this car. I haven't had any issues yet as far as legality. Also, in the interest of asthetics (and laziness), I don't want to add an aftermarket switch in the cabin which will look out of place. I'd add an OEM switch but it just sends a signal to the BCM to activate the fogs. Too complex (and expensive for reprogramming) for my blood. Thanks again to all and take care.

I see the sense for hi with low.
My 1965 vehicle has it, albeit currently using H4 outers but on full-time low beam.
I decided to keep that feature after replacing my BMW inserts which were dedicated H1 lows (as on their 3 Series (323?)). It was the traditional 4-headlight with outer hi/low.

It was also something I had on my rally car. It caused huge argument amounst rally regulators and authorities.
Guess who won that argument too? (Too many idiots in the wrong places. FIGJAM again!)