H4 Headlight Relays for Dummies

[kyngfish]

Hi all,

Can anyone point me in the right direction to installing relays for my new H4s? I assumed they were plug and play, but reading through old threads, the consensus seems to say I should install relays.

Assuming I know pretty much nothing about how car electronics work, aside from basic circuit principals like power and ground, can someone point me to where I can get a quick education? (For example, I have no idea what a relay is or what it does).

Also, how dangerous is it to run the lights without relays in the interim, while I figure all of this out? Do I need to put the sugar scoops back in?

Thanks,
Martin

[darrin]

Martin -- as long as you're not going with high wattage bulbs, you should be fine for the time being with standard h4 bulbs. Issue here is that, as built, all of the headlight current runs through the high beam switch on your turnsignal. This has been known to distort the high beam switch and cause you to randomly flash folks while driving. A relay is, in essence, a switch that is triggered by another circuit. You'd use the relay to bypass the high current connection through the turn signal/high beam and instead use the turn signal/high beam to power a low current circuit that "triggers" the relay to turn on/off the high beams (and headlight switch to turn on/off the headlight circuit.

Fortunately, there's an EASY solution -- our host sells a 911-specific relay kit that has exactly what you need to install the relays with (for me) easy-to-follow instructions -- here's a link Headlight Relay Kit JWST911HLPR - JWest Engineering - JWST-911-HLPR | Pelican Parts)

[kyngfish]

Thanks!

That's what I was looking for, the links in the old thread didn't take me to it, and I have a lot of trouble finding stuff at our host using standard search. Do I need to buy 2 or just one set?

[Joe Bob]

Google is your friend....

[kyngfish]

Darrin's explanation was better.

[Pazuzu]

Get the kit.
1 kit, it takes care of all lights.
It has 2 relays, simpler than Joe bob's drawing which has 4.

He has pictures, showing you which color wire to take from which fuse and where to put it. No sweat, even for someone who's a bit concerned about electrical work.

Edit: and for the $33, you'd have trouble piecing together enough stuff do try to do it yourself, if you were so inclined, so don't worry if you think it's too much...it's not.

[donporfi]

Use the advanced search feature and you will find a lot of posts regarding the installation of headlight relays.

Search for" headlight relay" with the Search titles only.

Or use these links

JWest headlight relay kit question

Daniel Stern headlight relay assembly and installation thread

Headlight Relay Kit (A More factory looking alternative?)

There are many more.

[kyngfish]

Ty Darrin and Pazuzu. Ordered the kit. Saw the kit on other threads but links lead to generic pages so I thought it had been discontinued. Appreciate the heads up

[Joe Bob]

You don't need a "kit". Just the relays, proper sized wire and connectors. Your local Manny, Moe and Jack has them.

[DRACO A5OG]

I did Joe Bob's diagram but place one relay for each set of beams i.e. One for High One for Low. BUt I like his diagram as it will only effect one circuit if only one light goes. Nice M

[Quicksilver]

Like Joe Bob I never understood why people think they needed a kit. Relays are easy.

All you need:
- A relay need a ground. (#85) Lots of choices where to connect to but there is a factory ground post right in front of the battery.
- A relay needs a supply of power. (#30) Battery is right there so get a crimp on "loop" connector and connect to the positive battery connector.
- A relay needs a switching source. (#86) Use the output connector of the headlight fuse as it will turn on when the switch is turned on.
- A relay needs a load to control. (#87) Hook up the wire going to the headlight to the relay output.

Other then this all you need is a fuse on the supply power and you will need a 2nd relay because you are dealing with the low beam and the high beam separately.

[Joe Bob]

I run retina burner bulbs. The extra relay=peace of mind and wear on the headlight switch and stalk which are uber pricey.....

[DRACO A5OG]

Originally Posted by Joe Bob

I run retina burner bulbs. The extra relay=peace of mind and wear on the headlight switch and stalk which are uber pricey.....

How many watts M?

[Quicksilver]

Here is my setup. . .


It is a simple aluminum plate mounted to the next two fender bolts in front of the stock fuse panel. It uses very commonly available relays so they can be replaced for nothing at any parts store. It uses the fender mounting point as the relay's ground and it has thermally resetting circuit breakers for all the relays. I have Lights (Yes they are that big!) so I added much larger wire from the relays to all the lights.

Other then the oversize wires all of this can be removed in about 20 minutes and no one would be the wiser.

[Joe Bob]

160 high beams and 120 lows. I took off the hood mounted driving lights, also 160 because they seemed to attract asswipes that back up their Prius's at Homey Doh.

[DRACO A5OG]

Holy Poop Batman, hate to be in front of you in the hood

[Quicksilver]

Originally Posted by Joe Bob

160 high beams and 120 lows. I took off the hood mounted driving lights, also 160 because they seemed to attract asswipes that back up their Prius's at Homey Doh.

You don't have enough lights until it stalls the engine when you turn them all on at idle!!!





(BTW - Everyone knows the correct term is "Home Despotism".)

[kyngfish]

Appreciate the detail. As much as I need to further my electronic education is rather get the kit in quickly and easily while I run through the litany of other minor projects... Unfortunately with a new baby and a full time job I have about 4 hours a week to dedicate to car projects.... 😬

[uwanna]

Just to demonstrate the effectiveness of using relays, before adding the relays when I turned on my H1s my voltage would drop from 13.2v or so down to around 12.7v to 12.2v
The voltage drop is due to all the wiring and contacts in the circuit causing increased resistance. The wiring goes through the ign sw, light sw, column flasher sw, and fuses before reaching the headlites! That's a lot of wire and contacts to develop resistance!
After relay install, with lights on, it stays constant at 13.2v. Enough said!!!

I agree with Quicksilver and Joe Bob on fabbing your own setup. Just bought a couple of standard
headlite relays, sockets, fuse links, and some wire, easy peasy!

Get a couple of these ,some fused pigtails and some extra wire and you've got all you need.
https://www.amazon.com/Auto-Truck-Relay-Socket-SPDT/dp/B007JPPQH6/ref=sr_1_20?ie=UTF8&qid=1470702625&sr=8-20&keywords=headlight+relay

[donporfi]

Joe Bob
I do not understand your diagram. Can you please explain?
According to Quicksilver 85 should be ground, 86 from fuse box, 30 from the battery and 87 to the headlight.
The 10 amp fuses are enough for your lights ?
For the Highs you have total 320 Watts and the lows 240 watts total ?
or total for the highs 160 watts and 120 watts for the lows ?
Meaning you have 160/120 watt H4 bulbs or 80/60 H4 bulbs.