Relay headlights

[Snitty]

Tonight, I wired my headlights through 2 relays... some time back, I converted to H-4 style headlights for the ease of changing them, and the variety of bulbs.... but the high output bulbs were makin my headlight switch VERY VERY hot... and i was afraid of burning something...

Even if you don't have an H-4 conversion, I highly suggest wiring your headlights through relays... I got AT LEAST a 20% increase in light output and minimized the current draw going through my headlight circuit.. the headlights are now recieving direct 12v power from a much better and more reliable circuit... I have done this on other vehicles before and have ALWAYS noticed a good improvement in light output...

total mod cost.... about $15
total mod time... about 1 hour
total satisfaction... total satisfaction

If you want to do it, and are afraid/confused of relays and wiring.. I could toss a plug-n-play kit together... I was actually thinking of doing so to sell to ricers on ebay... they are always burning out switches and harnesses around here because of their fancy colored, high draw headlights not wired right...

[Ragtopman]

Do you have a diagram you could post. I am about to wire a pair of 150w **** Cepek off road lights. I want to use a relay thinking of a 30amp from Radio Shack. What gage wire do you recommend?


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[XJNick]

Hi,

I'd say use 12 AWG wire, 10 AWG can also be used but is overkill. Note that this large size wire only needs to be used on the switching side of the relay (i.e. pins 30 & 87 or 87a on any standard automotive relay).

The coil side of the relay (pins 85 & 86) carry just a small amount of current so any wire size 20 AWG and up is fine to use. 18 AWG is probably best.

-Nick

[Craig]

Snitty...did you wire the relay through your existing headlight wiring or did you re-route the wiring directly off the battery?

[wm69]

I know absolutely nothing about relays or how they work. Anybody want to give me the "you're a dumba$$" 2nd grade version of how to do this. I've got 2 sets of KC's and am fixin' to ungrade to the H4 headlights and think this might be a good idea. People have suggested it but I've never really known what they were talking about. Thanks!

[jay79cj7]

Relays come in various types, but the basic, $5 at radioshack model is probably what you want to use. A relay turns on and off one circuit based on whether another circuit is on or off. Basically when you have a 12v drop across one set of terminals, the other circuit closes. When you don't have 12v, the other circuit is open.

You run the hot from the battery to a terminal on the relay. The matching terminal goes to the headlights. So now when the relay is turned on, the headlights have the power going to them. To turn on the relay you hook the hot from the "on" position of your headlight switch to one terminal, and ground to the other. You turn your switch on, the current runs to ground through the relay, which flips the switch to turn on your headlight circuit... You have now wired your headlights so the same current that flows to the lights doesn't flow through the switch.

Obviously you have to hook all 4 wires up to the right terminals, but there should be a diagram that accompanies the relay. There will be 2 circuits. One with a coil and one with a switch. The switch is the switched circuit. The coil is the controlling circuit.

Hope that made sense.

[Snitty]

i just used one side to power two relays... one for the highs, one for the lows.... the driver side lowbeam power wire turns on the relay that powers both lowbeams.... the driver side highbeam power wire turns on the relay that powers both highbeams... all grounds are wired back to a heavy common. I used two $4 relays from autozone... it does NOT have an 87a, but has two 87's... so i could use one for each side, so each of the total 4 headlight filiments has its own source terminal. I used a fused 10 gauge wire to provide batter power... then from the relays, i used 12 ga 4 wire trailer wiring to run to the lights, wired to new H4 harnesses.. i used the white, yellow, and brown of the trailer wiring, and pulled the green off to make a 3 wired strand.

[Snitty]

to wm69.... relays can be very very helpful tools... i don't wire anything anymore without them.

here is what they do... instead of running the power for a device through the switch in your dash... it will run through the relay... if you have 4 100 watt lights on a light bar, you dont' want that current running through your dashboard... you are liable to be chasing melted wires and burning your fingers on a red hot toggle... if you run a relay... that relay, which is designed to handle higher current, will take all the current... the dash switch will simply be handling enough current to activate an electromagnet inside the relay which closes a switch inside to complete the higher draw circuit...

if you want to use them for their basic use... follow this simple list...

85- power from switch (or former power wire)
86- ground
30- fused, direct 12v power, usually 12 or 10 gauge
87- device to be powered when the switch is on
87a- device to be powered when switch is off

not all relays have an 87a... and if you are simply using one device, you need not use 87a at all... it is simply used as a "selective option" so you can have the option to power one device with the switch on, and one always powered with the switch off...

some relays are directional... and the 85/86 poles must be wired in a certain polarity... if a relay doesn't work, and seems like it should... always switch the 85/86 poles to see if that takes care of the problem.

a common error that people make while hooking up relays is forgetting to ground the relay coil, which is the electromagnet in there... when you flip the switch, the relay needs THAT power, and a ground in order to activate the internal switch... remember that both the relay AND the final device need to be grounded