Technical Headlight relay question

Good morning, just a quick question re: headlight relays. Is it recommended to use…

two: one for the left and right low beams and one for the left and right high beams?

two: one for the left low and high beams and one for the right low and high beams?

or four: one for each left and right low and high beam?

I did use the search and came up with quite a few posts already, but I’m seeing different wiring diagrams for both configurations, just wondering which was is best or if it even matters. Thanks

 

One relay for both low beams, and another for both high beams, is the only thing that makes sense to me.

Or just use a good switch and big enough wire, and don't bother with the relays. I've never used them, and can see fine at night.

 

Good grounds make as much difference as anything. I used 16 gauge wires for high, low and ground, and ran the grounds all the way back to my main bus bar. Each light has its own ground and feed. Never had a bulb go bad in 20 years and are still as bright as the day I installed them.

 

16 gauge wire is a little light for lights! Pun intended! Lol I never use any thing smaller than 14 gauge on cars. OEM uses lighter wire, for saving money, but the difference in the cost of 16vs14 gauge at the parts house is not that much!






Bones

 

Voltage drop is what you're concerned about. For a 10 foot run to both headlights (about 10 amp load), with 14 gauge you lose half a volt, with 16 gauge you lose over 3/4 of a volt.

Either will work, but the larger the wire, and the shorter the run, the brighter your headlights will be...with or without a relay.

 

The kit I bought used one relay for low and one for high beams.

 

The light switch is a throw and so is the high beam floor switch..

I use #12 stranded for head lighting..

You could run knife switches..

 

Energize both coils when using high beams. Low N.C. High's N.O.

 

On a four-light car you really only need one relay at most. Most OEM light switches have a 15 amp circuit breaker built-in, which is big enough if using OEM-type 50/35W sealed beams so no relay required. You do want to use a minimum wire size of #14 to the lights, 12 is better, with a #10 to feed the switch. A lot of headlight relays are installed to overcome too-small wire from the switch; voltage drop is why your lights can end up dim.

Now if you use aftermarket halogens with a 55/60W low beam rating and 60W high, you do need a relay and the internal circuit breaker won't be able to carry the full load. The low/high outer lamps will draw a maximum of 10 amps, they can remain connected to the switch. Connect just the high beams (which also draw 10 amps) through the relay, controlling it off the high beam feed for the outer lights. Power to the high-beam-only lights through the relay should be a separate circuit.

 

I bought an old aftermarket headlight relay for a 2 headlight system, it has heavy duty contact points and a glass fuse inside. I used a rebel harness (I believe it's a 16g wire to lights, if I remember correctly), a 10g wire from the battery to the relay to Silver Star sealed beam halogen headlights. I'm using an NOS headlight switch and wanted get some load off of the contacts. I bought a few for other cars, even the '28 is going to have a sealed beam.

It's 2 relays in one. One contact set for low and one for high.

 

That's the only reason to do so no matter if switch is ancient by design or new with barely any ability to carry load requirement.

 

Silver Star sealed beam halogen headlights. Used in my ot stone stock wired 72 Comet and was suitably impressed with the "spread".

 

There are lots of ways to connect it, done well most can be good so I'm not gonna add much to the previous suggestions now.
But no matter how you do it, feed it through at least two different fuses (or breakers), either separate low/high or separate right/left. If it all comes from a single feed one single problem can knock out all light, and I think too many of us knows how fun it is to try to solve electrical issues on the side of the road in the middle of the night. With separate feeds you can lose one and still have enough working lights to get back home, and can worry about fixing it tomorrow.

 

I just got done building a relay harness for my truck. I'm using one relay for highs and one for lows. Feeding power to each relay from a fuse block with 10 gauge wiring out to two 14 gauge runs to each light. The relays I'm using have two 87 terminals, so one output terminal for each side. Using the outputs from the dimmer to trigger the relays for each circuit.

 

Why the hell do you clowns get so frigging far away from the op's question every time someone asks a freaking simple question? Especially when you are clueless as to why he wants to run relays. The number of half baked idiotic answers is astounding .

The answer is as Jim stated in post 2 one relay for low beams and one for High beams.

Put the relays on the inside of the core support or on the inner fender close to the front on fat fenders.
They will do what you want them to, protect your existing switches and wiring if you are running extra bright Halogens.
I put relays on my headlights because when I ran lights with enough power to see the drunk walkarounds staggering down the road in dark cloths at 11:30 at night the amp draw from those lights was seriously hard on dimmer switches.

 

You sure that both "87" terminals are the same? Usually there is an 87 and an !87 (!87 is opposite of 87, meaning one is on with relay coil not energized, the other being on with relay coil energized.

 

Depending on rating of relay contacts, you could get away with one relay that has 87 and !87 contacts. Wire the hi beams to 87 contact, and low beams to !87 contact. I would look for a 30 amp NC / 30 amp NO contact rated relay at the minimum. Another trick would be to put capacitors between #30 and #87 and #30 and !87. 1mfd @ 25 volts should be good. The capacitors will prevent arcing of the relay points when switching relay on and off.

 

If you pencil out the additional current draw of Halogen versus Tungsten they are still well within the design margin of existing wiring harness and the rest of it. This makes sense if you think about it, the manufacturers would have never offered them for replacement in the first place if they weren't. I've run Halogen for years in a generator equipped system and they work great for hours on end road trips with no problem.

Any vintage car or truck will have seriously defective grounds, cables, and connections by now that need attention, Halogen headlights will offer no improvement in that situation, maybe even worse. The deal with lighting, even a slight voltage drop will cause the headlight output to drop off a cliff. I like and use the relays but they and the headlights will work so much the better when the underlying defect is remedied in the first place. If headlights are dim or flickering it's a safe bet everything else is probably being starved for current too.

Remember Bruce Lancaster here said it best "Clean & tight electrical connections = Happy electrons". He was right!

 

To answer your original question.....1 relay for both low beams, 1 relay for both high beams.

 

THANK YOU, 48

Ben

 

I like relays for vehicles that do a hell of a lot of night driving. I've seen too many burnt, pitted, failed light switches from repeated, full power loads. There's a correlation between how many times the switches are cycled and how soon they fail.
If your car is a low mile cruiser always home before dark, not using headlight relays may not be a problem for a long time if ever.

 

Now if you did that, wouldn’t the NC contacts have the lights on all the time?

I assume you use the headlight switch to energize the relay, at the relay you have power ready to go.

Without seeing it on paper drawn out, I get confused

 

BTW, I wanna be a clown!

 

You'd also need another way to switch the "main power" coming to that relay, yes.

 

So another relay, etc. kinda leads back to using two relays

I did like the suggestion/comment about separating each light. Might be over kill, but one issue won’t take out both lights, unless the switch is the issue.

 

Some guys just love relays.....

 

I guess I may be one of those “ clowns” you referred to, as I did drift away from the OPs question. But I saw something that lit the light bulb in me with the 16 gauge wire thing. So I thought I would speak up. Now, my degrees and certificates and 33 years of maintaining $2,000,000 pieces of equipment should take me out of clown status, I would hope.
But I take offense with you calling my HAMB friends “ clowns” . I guess some people just can’t help being assholes!










Bones

 

The relay is energized by a dimmer switch. The #30 terminal gets power from headlight switch terminal labeled headlights. When dimmer switch is open the low beams have power, when dimmer is closed the high beams have power.
One side of dimmer switch gets power from #30 terminal, with the other side going to #85. #86 gets grounded.

 

I see!

 

Okay So I finished wiring up the relays and I’ve got no headlights or highbeams at all. I used two relays, one for the high beams and one for the low beams. Here’s is how I wired them-
12v from starter relay (15 amp fuse inline) to pin30
Headlight source wire from wiring harness goes to pin 86
Pin 87 goes out to headlight
Pin 85 is grounded to a screw in the rad core support
87a is not used

I checked my grounds, they are good. I verified that I’m getting 12v to pin 30

All I can think of is that the relays are junk, the molded plastic connectors they came with are junk, maybe I’ve got 85 and 86 backwards, or maybe I was supposed to use 87a for something?

can someone review my wiring and let me know if I’ve got it right?

Here are the relays I used:

ONLINE LED STORE 6 Pack Bosch Style 5-Pin 12V Relay Kit [Interlocking Harness Socket Holder] [14 AWG Hot Wires] [SPDT] [30/40 Amp] 12 Volt Automotive Relays for Auto Fan Cars https://www.amazon.com/dp/B01KVZ2MU...abc_94WDK5T9X04QBP538FBZ?_encoding=UTF8&psc=1


Thanks!