low beam + driving / fog light wiring (revisited)

[rsporsche]

i have been sorting through the wiring to add relays and fuses to the low beam lights and add a switch for the driving / fog lights.

i will be using
(2) hella 933332101 relays - these are 4 pin SPST
(1) hella h84989011 relay socket - for the fog light ... i will be using an e9 socket for the low beams next to the battery
(3) bussmann maxi fuses + waterproof fuse holders with 20a fuses (i will explore if i need any larger fuses - but want to start with what was recommended)
12 gauge wiring from the battery to the relays - thru the fixtures - and to the grounds. wiring back to switches will match existing ... i am guessing that i will use 16 gauge ... since the majority of the power will be running from the battery to the lights ... only the standard fuse power will operate the relay to power the lights.

i am sourcing the relays, fuses and sockets for this project and the window motor relays thru Summit Racing (the hella relays are about $3.50 each and the sockets are about $1.15 each. the fuse holders and fuses are about 15 bucks each. if i used a different fuse type, that would be much less expensive.

i have attached a wiring diagram, based on the original 2800cs diagram from the blue books - coordinated with Stevehose's diagram of an old thread. (thanks for sending me the link Steve). For the driving lights, i am using one of the old green 'round' switches mounted on the '74 under steering wheel panel. i haven't looked at this switch requirements or how they have been wired ... i would appreciate some of you more proficient automotive electricians to look at what i have drawn and give me some recommendations.

cheers
scott

 

[sfdon]

Wire pin 87 of the fog and low beam relays the same as the high beam relay-
2 wires at the terminal

 

[Stevehose]

So are you doing driving or fog lights, in other words do you want them on with the high beams (driving) or on with low beams only (fog)? Or on whenever you press the button? I have mine wired for on with high beams but the switch cuts them off when not appropriate to have on with the highs. When i flash with all beams on its like a cannon going off

 

[sfdon]

You might also consider wiring the fog relay ground to the hi beam ground

 

[rsporsche]

thanks for the comments guys - yes, i will tie each of the driving lights to the ground on their respective side. i also have split the wire from the relay, which is probably what i would have done anyway - question for you Don, Hella makes a 12v relay that has dual 87 pins ... would that be preferential for this application? (not a 5 pin 87 / 87a relay).

good pickup Steve - i have 2 drawings, 1 with fog light, the other with driving light. the driving light version doesn't connect to the fog-light cutoff. i made the split wire revisions suggested by Don.

 

[Ohmess]

Scott -- the way you have the switching wired, you will be able to turn on the driving/fog lights independently of the low beam and high beam lights as long as the ignition system is on.

This is fine, but I believe in most states it is illegal to have three sets of lights above a certain output illuminated at the same time. This is why most modern cars are wired to turn off the high beams if you engage the fog lights. I'm not sure how these rules apply to driving lights, perhaps because they are not common in the US.

 

[Stevehose]

If you do it independently then you'll be reaching down to the button very frequently to dip them when traffic appears. Suggest wiring them to come on or off with either hi's or lo's and use the switch to keep them off when needed.

Scott -- the way you have the switching wired, you will be able to turn on the driving/fog lights independently of the low beam and high beam lights as long as the ignition system is on.

This is fine, but I believe in most states it is illegal to have three sets of lights above a certain output illuminated at the same time. This is why most modern cars are wired to turn off the high beams if you engage the fog lights. I'm not sure how these rules apply to driving lights, perhaps because they are not common in the US.

 

[Ohmess]

You can do what Steve suggests by running power to the fog/driving lights from an 87/87a relay on the high beams. With an 87/87a relay, power to the 87 terminal is routed to the 87a terminal whenever the relay is not engaged. You could use this as the source of power for the fog/driving lights relay rather than powering the fog/driving lights off the battery directly. When you switch on the high beams, the 87/87a relay will disconnect power from the 87a terminal.

 

[rsporsche]

actually, that is a good idea ... although i was going to keep using the round relay i have for the high beams. i guess i could move that to the driving lights + guy another round can relay + put a new 5 pin SPDT relay in it. i know there is a connector for foglights off of the high beam relay ... but i don't see that it is a 5 pin relay ... the connector comes off of the 86 pin. no idea how it works or just that perhaps it sent a signal to the fog lite relay to turn it off. but since i don't know how they would have done it ... i like your suggestion of the 5 pin ... i will look into this a little. might have to ask a question or two to make sure i got it right.

 

[Ohmess]

I actually have the aux fan in front of my radiator wired this way. When the a/c is on, the fan always operates. When the a/c is off, the 87a terminal sends power to another relay, which turns on the fan if the coolant goes above a certain temp (85 degrees celcius, I think).

 

[rsporsche]

i've given this a little thought ... and my electrical ignorance might show thru in a few seconds. that being said, i have often heard that somebody teaches best what they need to learn most (or something like that).

so with high beam relay as a SPDT (single pole, double throw or a change-over) relay - if i have the high beam switch is on, terminal 87 is powered (high beams are on) - no power is going to the other relay (thru 87a) - that's ok. when the high beams are off, terminal 87 is then powered off and 87a is powered - sending power to the fog light relay. this would attach to terminal 30 of the fog light relay (instead of direct battery power) ... and the switch would control terminal 86 of the fog light relay and determine whether the fog light relay transfers the power to the fog lights. this is represented by the fog light relay2 picture. this seems like a relatively elegant solution - does everybody agree with this operation?

so now for where my ignorance might show up. the factory high beam relay is a SPST (single pole, single throw) relay. if you use the factory fog light connector (powered off of the high beam relay - terminal 86) ... with the high beam switch on, there is power in this wire (the relay is connected and the high beams are on) ... this puts power to terminal 86 of the fog light relay which is the same as the fog light switch being on (isn't it?). so my diagram doesn't quite work does it ... as the fogs would be on with the high beams. so i guess i have the intended use of this connector incorrectly used or the misunderstanding of what happens electrically. any ideas?

 

[restart]

This is fantastic! Thank you for sharing!

 

[rsporsche]

anybody have a comment on my questions on the fog light relay wiring? i'm thinking that the first one with the double throw (SPDT - changeover relay) is the way to go, as i'm not sure the lower diagram works ... don't think the driving / fog lights will turn off with the high beams on.

like i say, i'm a little automotive electrically challenged, but if you consider the 2nd pic. if the fog lights are switched on, and you flash the dip switch or turn the high beams on, power will flow to the fog light connector ... which is the same circuit as the switch power to the relay ... that won't power it off ... not sure what happens with power flowing from both sides. any thoughts?

 

[HB Chris]

In lower pic fogs will always be on with hi beams, pic one looks doable.

 

[rsporsche]

In lower pic fogs will always be on with hi beams, pic one looks doable.

great - thanks ... that's what i thought and works with the types of relays that i ordered. when i get my car back, i will dive in while the grilles are out of the car.

 

[aearch]

ill get the oem here the way to wire
send a note ill forward to you [email protected]

 

[rsporsche]

Alan,

i have no interest in wiring it the way it was done originally. i don't want to melt the light switch with the power drain of high voltage halogen lights and thin wires. i want brighter lights without the risk of damaging electrical components.

 

[aearch]

can someone post the answer to the solution above from restart

 

[Markos]

can someone post the answer to the solution above from restart

@restart doesn't have a question or a solution above. @rsporsche didn't really have a question (or solution) either, just a set of ideas. What is your lighting goal? I noticed in another thread that you want your fogs to run independently of your low beams. I have to ask why?

Here are my general opinion on how lights should function, with the intention of lighting the road, not looking cool:

1. Headlight switch in parking light mode engages parking lights and/or city lights
2. Headlight switch fully engaged turns on low beams
3. High beam switch engages high beams, low beams (and fogs) turn off
3a. Optionally, low beams stay on
5. Driving lights come on with high beams
6. Fog lights come on with low beams

Regarding #5. If your driving lights are independent of your high beams, that means that you are going around a bend and have to reach for a switch on/under your dash to disable lights that are more blinding than a high beam. You want to be able to quickly disable your driving lights with your high beam switch. Also, driving lights are for distance. If your interest is lighting, there is no real reason why you wouldn't want them on in conjunction. Driving lights should be mounted above the bumper.

Regarding #6. Unless you are driving through pea soup, there is no reason to have your fogs run independently from your low beams. There are instances where it is so foggy that your low beams are bouncing off the fog, and the independently lit fog lights are cutting through the fog near ground-level. For that reason, fogs should always be mounted under the bumper. Unlike driving lights, if you do mount them independent of the low beam switch, there are no implications related to oncoming traffic. Fogs should use a low wattage bulb. Their value is a wide low pattern, not brightness.

 

[Ohmess]

Also, the reason fog lights are wired in US cars to switch off when the high beams are illuminated is to comply with a federal regulation limiting the number of forward facing lights than can be used at any one time.