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Old 11-20-2007, 11:18 PM   #1 (permalink)
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Default Connect your headlights straight to your battery

I ran some higher wattage Nokyas a few years ago. Didn't upgrade the harness. Ended up melting the plugs. Went back to stock bulbs and everything was fine. But then the bulbs started winking on and off randomly, and burning out quickly (3 months). Figured it would be a good time to upgrade the wiring. Didn't want to put in a HID kit (cause of glare). Decided to wire the headlights directly to the battery, and run relays to control them instead.

Disclaimer: Not a complete DIY, cause I didn't build my own harness. Found a plug and play one on ebay for $13, and used that instead. Also, I'm not an electrical expert, so my terminology probably isn't 100% correct. And apologies if I sound redundant to anyone with more experience than me. Oh, and this is mainly for an EG Civic, though it should work on any other car that uses H4 / 9003 bulbs.

Why relay your headlights? (from vintagewatercooleds.com)
well - if you have aftermarket light housings, or are running higher wattage bulbs, then you are exceeding the capacity of the factory wiring in your car. Relaying the headlights makes the path the power has to take much much shorter. In stock form, the power goes from the car battery back to the fuse panel. Then it goes through a relay that turns them off when the key is turned. Then it goes through the fuses, then up to the headlight switch. It goes right through that switch (ever feel that switch get warm?) Then, it goes back into the wiring harness and back up to the front of the car to connect to the headlights. All of this wiring is just the right gauge for stock bulbs. All of this wiring is 15-25+ years old.

Long path.

So - relaying does this... The power goes from the battery to the fuse, then a few inches to you're relay box. Then it goes to the headlight. MUCH shorter. The advantage here is that since you can use new wiring, you can make it a larger gauge than the stock wires are. And you can happily run 110W bulbs all day long and not fry wires.

Sites to visit
http://www.vintagewatercooleds.com/t...Wiring_Diagram
http://www.se-r.net/electrical/wiring_relays.html

How Relaying Works
In short - you wire your headlights directly to your battery. But to make sure that you can still turn them on and off, you put a switch in the line. And to make sure you can still turn them on and off like you would normally (via the stock control inside the car), you use a special kind of switch, one that reads your stock wiring. When you flip your headlights on inside the car, the switch will read the current coming from the stock harness, and it'll flip on the connection between the headlights and the battery. Anyway, the switch is called a Relay. That's all there is to it, if you're just running low beams. If you want high beams, you'll have to add another relay.

First thing to do is to familiarize yourself with the H4 bulb, and with which wires on the stock headlight plug/harness control which function:

image credit vintagewatercooleds.com

On the passenger's side of an EG civic, the headlight plug looks like this:


The red/white wire at the back of the plug is the low beam wire. Red/blue = high beam. Black = ground.

Next, familiarize yourself with relays:


Relays have four connectors labeled 30, 87, 85, and 86.

30 = POWER IN from battery
87 = POWER OUT to headlights
85 = SIGNAL IN from stock headlight harness
86 = GROUND from stock headlight harness

When there is no signal from the old headlight harness, 30 and 87 are not connected. When there is a signal from the old headlight harness (When 85 reads a current coming from the stock headlight harness) it flips a switch and connects 30 and 87, allowing power to flow from battery to bulb.

Note that the connectors don't have to be positioned as they are in the diagram above. They can appear in different combinations:


Check your own relay to see which connectors are which number. Important thing is just to remember what 30 is, and what 87 is, and wthat 85 is, and what 86 is. The function of the connectors never changes.

Text Version of What You Want To Accomplish
You want to run a wire that connects the battery to the low beam prong on both H4 bulbs. And you want to run a wire that connects the battery to the high beam prong on both H4 bulbs. In each of those cables, you want to put a switch. You want the switch that is in the wire that goes to both low beam prongs to read the low beam signal off the stock headlight harness. When it reads no signal, you want the switch to remain off. When it reads a signal, you want the switch to connect the battery to both low beam prongs. Ditto for the wire that connects the battery to both high beam prongs. Oh, and you want to ground everything, too.

Diagram of How to Accomplish It
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Old 11-20-2007, 11:21 PM   #2 (permalink)
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Cheat
Here's where the write up becomes not a write up, cause during research I discovered that you can buy harnesses pre-made, plug and play, and I scored an APC H4 upgrade harness off ebay for $13. Normally around $50. Do a search for "APC H4 Upgrade harness" and you'll find it. You can also buy one here for a lot more: http://performanceparts.com/part.php?partID=23099

So, as far as building the harness...you're kinda on your own for that one. But if you go to these two sites:

http://www.vintagewatercooleds.com/t...Wiring_Diagram

and

http://www.se-r.net/electrical/wiring_relays.html1

You should be able to figure it out on your own.

Installing the harness
The APC looks like this:


Chuck the instructions. They're written in very bad Engrish.

Now:
- Disconnect the negative end of battery.
- Unplug the stock headlight harness from the bulbs.
- Wrap the drivers' side stock headlight plug / harness with electrical tape and tuck it away someplace (you won't be using it).
- Wrap the high beam plugs on the APC harness with tape to seal them. You can tell the high beam plugs because they don't have a low beam wire running to the top of the plug. You won't need to use them in a headlight setup that only uses one bulb per headlight.
- Plug the relays into the APC harness.
- Plug the APC harness's headlight plugs onto the headlight bulbs on the car.
- Connect the passengers' side stock headlight harness plug with the stock harness connector on the APC harness.
- Ground both the drivers' side and the passengers' side ground of the APC harness somewhere on something metal.
- Connect the APC harness to the positive end of your battery.
- Test the thing.

Low beams:


High beams:


Yup, everything works.

I just kind of shoved everything in and taped it out of the way. Later I'll take the bumper cover off and rout the harness out of sight.




Now, theoretically, if your stock harness was fried, installing a relay harness should make your headlights brighter. Should deliver more power in a more direct line. And you can also run higher watt bulbs without worrying about melting issues, cause of the thicker-gauge wires.

Me, I didn't notice a difference in luminosity.

Stock harness:

Only passengers' side light in the comparison, cause I had taped and tucked the stock drivers' side harness and plug out of the way.

Relay harness:


No difference in brightness, but the good thing is that my headlights don't wink on and off randomly anymore. And I can stick in brighter bulbs now.

Good luck. Any questions or suggestions, let me know.

Last edited by limitk7; 11-20-2007 at 11:26 PM.
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Old 11-21-2007, 04:13 PM   #3 (permalink)
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very nice, I did to mine awhile back, but I was too lazy to write a diy
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Old 11-26-2007, 09:29 AM   #4 (permalink)
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your underhood looks like a damn rainbow yellow, blue, red, silver, black, orange, white, and green. thats impressive
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Old 11-26-2007, 09:40 AM   #5 (permalink)
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not bad. i did this a few years ago on my 97 coupe.

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Old 11-28-2007, 06:17 PM   #6 (permalink)
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your underhood looks like a damn rainbow yellow, blue, red, silver, black, orange, white, and green. thats impressive
Who needs wiretucks...
...or engine brite, for that matter
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Old 11-28-2007, 07:18 PM   #7 (permalink)
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nice diy.
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