DIY: Relays for dim headlights

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iceblue
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DIY: Relays for dim headlights

Post by iceblue »

Ok so this seems to come up a lot and there are lots of links and circuit diagrams, but not everybody knows how to read a circuit diagram so I thought I would do a quick DIY (with pictures) on how to fit relays to your headlights. This post was done in a hurry but I will edit it to add more info and better pictures if necessary. Also if anybody wants to contribute, correct or suggest anything please do.

Why fit relays?
With age, the wiring in your car begins to lose conductivity and this results in less current flowing through you headlight bulbs. In addition to this the factory wiring is very thin and runs quite a distance (from the battery to the fuse panel to the headlight switch and then to the headlights via the scenic route) and this increases the total resistance in the wire.

Fitting a relay shortens the distance from the battery to the bulbs and using nice thick wire means less power is lost in the wire itself and more is delivered to the bulbs. This results in much brighter light output.

Can't I just use 100W/130W bulbs instead
Well you could but apart from the fact that I've heard rumours that this is illegal, you also run the risk of melting you headlight housings or the insulation on your headlight wiring. It may have worked without any problems for your friend, but do you really want to take the risk? 100W and 130W bulbs draw approximately twice the amount of current as 55W bulbs. Your factory wiring was chosen with this in mind. Also as the wiring gets older and becomes more resistive, more power is lost in the wiring. This power is converted to heat which can melt your insulation.

What do I need?
The following items are for doing one set of lights (i.e. left and right high beams or left and right brights). If you are doing both sets just double up (except the earth cables).

1x 4 pin relay (25A minimum). Avoid the cheap ones. I got a Hella for R25 after buying a cheap one for R15 which did not work.
8x female spade connectors (I dont remember the size but they need to fit onto the relay terminals)
4x male spade connectors (same size as females)
1x ring terminal (big enough to attach to positive terminal on battery terminal - see pictures)
1x inline fuse holder (look for one with a waterproof casing and thick cabling)
1x 20A fuse for fuse holder
2m 12 gauge wiring
0.5-2m 12gauge wiring in a different colour (used for earth so brown or black would be a good idea)
7mm diameter heatshrink (can be replaced with insulation tape if necessary)
Crimping tool

Image

Building the wiring harness
1. Run the 12 gauge cable from the headlight furthest from the battery, along the wiring harness until the battery positive terminal to see how long it needs to be (mine was about 1.7 metres). The remaining piece of wire should reach to the nearby headlight connector.

2. Cut the wire at the point where it reaches the positive battery terminal. Strip about 5mm of insulation off the ends of the wire and attach a female spade connector to one side of each of the two pieces of wire.
Image

3. Take the two ends of the two pieces of wire which have not had terminals put on them and place them into one female connector and crimp as shown below. If you cannot get them into one connector you can give each one its own female connector and then connect them together using the piggyback connector shown in the very first image (the one on the left of the relay).
Image

4. Slip some heatshrink over again and shrink it with a lighter. If the heatshrink wont go over the two wires you can stretch it using a long nose pliers or something similar.
Image

5. You should now have a single cable with 3 connectors on it.
Image

6. If you fuse holder came with one piece of cable connected to both ends, cut it about half way through the cable. Strip 5mm off both endsd and attach a female connector to one end and cover with heatshrink. On the other end, slide about 2cm of heatshrink over the wire all the way down to the fuse holder (do not shrink it yet), then crimp the ring terminal onto the end of the wire. Slide the heatshrink over the crimped section of the ring connector and shrink it.
Image

Fuse holder with terminals connected and heatshrink in place (note: this was not a waterproof fuse holders so I put the fuse in place and covered the entire holder in silicone to seal it).
Image

7. Go to your car and check which wire is supplying power to the headlights. You may need a multimeter to check this, otherwise just check which wire runs to the bulb. You need to make sure you find the positive wire. The ground wire is usually brown so the wire you are looking for should not be brown (we will deal with that one later on). The wire should be the same colour for both the left and right head light. Once you are sure you have the correct wire, start at the headlight furthest from the battery and cut it off about 5-10cm from the headight connector. Place a male spade connector on the end which goes to the headlight. The other end of the cut off wire can be insulated (with heatshrink if desired) as you wont be using it (thats assuming you are working on light furthest from the battery). Slide about 4cm of heatshrink over the male terminal, then connect it to the female connector on the long end of the cable made in step 3. Slide the heatshrink over both the male and female terminals and shrink it (don't set your car on fire!)

(note the harness shown below is not the same as the one shown above)

Image

8. Run the cable along your factory wiring harness back towards the battery and nearby headlight.

9. At the headlight nearest the battery, cut off the 12 positive headlight wire again like in step 7. This time you need to connect a male terminal to the end going into the headlight connector and a female connector to the end coming from the factory harness. The female connector will be connected to the relay to switch it on and off (explained later).

10. Connect the short end of the cable made in step 3 to the wire running to the headlight and heatshrink as in step 7.

11. At both the left and right headlights, use the different coloured 12gauge wire to create new wires running to ground. You can cut off the existing ground cable (usually brown) at the headlight connector (leave 5-10cm again) connect a male spade connector to the piece going into the headlight connector. Use a female to connect it to the 12gauge ground wire and find a place to ground it at (either all the way back to the battery or just onto the body nearby). Remember to do this at both headlights.

12. If you look underneath your relay, by the terminals, you will see each terminal has a number. Connect these terminals to the corresponding connections as follows:
30 -> female spade connector on fuse holder
87 -> remaining spade connector on harness made in step 3
85 -> female spade connector attached to positive wire from factory harness in step 9
86 -> connect this to ground

Image

13. Connect the ring terminal from the fuse holder to the positive terminal of the battery.

(ignore the badly connected red amplifier power cable! You're looking at the yellow wire)
Image

14. Put some insulation tape around the connectors of the relay so that it doesn't get wet and attach it to something so that it doesn't bounce all over your engine bay.

15. Put the fuse back into the fuse holder, and check that everything works fine.

16. Wait for it to get dark and go and have fun being able to see where you are driving again. :driving:
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Re: DIY: Relays for dim headlights

Post by BLiZArD »

+1
from every mk2 owner who knows exactly what you're talking about! :lol:
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Re: DIY: Relays for dim headlights

Post by Viral_88 »

Brilliant write up :type:

I did this 2 weeks back and just couldn't believe the results :cool:

This is definitely a must for anyone with dim headlights :bang:
Its simple, cheap and extremely effective !

Nice one iceblue
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Re: DIY: Relays for dim headlights

Post by iceblue »

Thanks. I'm hoping to post some better pictures and additional information soon (including before and after pics). I was just as impressed by the improvement when I did mine.
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Re: DIY: Relays for dim headlights

Post by marzbars »

I did mine on Saturday took up more thanhalf my day the longest process being to find a spot to mount the relays. I used the same write up to do my fogz using the park linghts wire from the wire and wow. Thanx for th great write up Ic blue. If you ever meet me make sure i buy you a drink
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Re: DIY: Relays for dim headlights

Post by Viral_88 »

@ Iceblue

Just for interest sake this is the diagram i used

Image

I'm sure with this diagram and your photo's it'll be a breeze for any wanting to attempt this
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Re: DIY: Relays for dim headlights

Post by iceblue »

GTS wrote:I did mine on Saturday took up more thanhalf my day the longest process being to find a spot to mount the relays. I used the same write up to do my fogz using the park linghts wire from the wire and wow. Thanx for th great write up Ic blue. If you ever meet me make sure i buy you a drink
Ya, the space between the battery and the headlight is quite tight. I ended up just mounting the relay to the back of the headlight with a cable tie. That drink sounds good! :drool:
Viral_88 wrote: I'm sure with this diagram and your photo's it'll be a breeze for any wanting to attempt this
Thanks bru. I actually wanted to put a diagram up but haven't had a chance. This is a great one actually so I think we will just stick with it :grin:
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Re: DIY: Relays for dim headlights

Post by playa4life »

Nice one!!! Ive been wanting to do this for ages now! Will this sort out my issue too? When my lights are on normal low beam and I pull back stalk to throw or to activate brights, as long as Im holding the stalk, but not pulling it back all the way by letting it click into place, the lights shine very bright, but the moment I pull it back all the way and the stalk engages and activates the actual brights then it goes a bit dimmer! I hope that made sense :oops: :oops: :oops:
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Re: DIY: Relays for dim headlights

Post by ANTONY JOHN »

ANTONY JOHN wrote:So maybe a new question for the guys that are clued up with relays and lights... :)
I have a 1991 MK2 GTi, which is infamous for lighting issues I believe.
My problem: When I flash brights, it's like day-light, amazing. But as soon as I turn the brights on (actually 'click' the stalk) the light fades drastically. The brights are on, but only produce about 20% of the light that it should. Normal driving lights could also be a lot better i feel. Especially with Nightbreaker globes.

I've been told to check the earth connections on the car.. Great, which ones and where are they. And do the lights have their own earth? I have sanded and cleaned the battery earth.

So I was thinking of adding a relay, but would it help. I mean is the problem the high beam circuit or the power circuit?

Any help would be appreciated, as I'm very confused. :oops:
I GET IT!! : :wink: I had the exact same problem! Upgrade the wiring and you're sorted.
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Re: DIY: Relays for dim headlights

Post by playa4life »

ANTONY JOHN wrote:
ANTONY JOHN wrote:So maybe a new question for the guys that are clued up with relays and lights... :)
I have a 1991 MK2 GTi, which is infamous for lighting issues I believe.
My problem: When I flash brights, it's like day-light, amazing. But as soon as I turn the brights on (actually 'click' the stalk) the light fades drastically. The brights are on, but only produce about 20% of the light that it should. Normal driving lights could also be a lot better i feel. Especially with Nightbreaker globes.

I've been told to check the earth connections on the car.. Great, which ones and where are they. And do the lights have their own earth? I have sanded and cleaned the battery earth.

So I was thinking of adding a relay, but would it help. I mean is the problem the high beam circuit or the power circuit?

Any help would be appreciated, as I'm very confused. :oops:
I GET IT!! : :wink: I had the exact same problem! Upgrade the wiring and you're sorted.
Cool! But when you say upgrade the wiring... what exactly do you mean? Follow above mentioned procedure??? :oops: :oops: :oops:
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Re: DIY: Relays for dim headlights

Post by ANTONY JOHN »

Yup, new wiring and relays. I went from 7V at the globe to 12V. I think I could get a bit higher with a new light switch though.. What car do you drive? A new earth cable could help things too. I got a length of battery earth cable from outdoor warehouse, works a treat.

Just make sure that when you are doing all the wiring your connections are proper! Solder or crimp properly.

Good Luck! :smile:
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Re: DIY: Relays for dim headlights

Post by iceblue »

Yes fitting the relays should fix that problem. I have the same thing happening with mine but haven't had time to fit the relay on the brights yet.

If you have fitted a relay, changing the light switch WON'T improve the voltage at the headlights. That is determined by the thickness of the cable you run and the quality of the relay used. (thicker cable will have less resistance and thus higher voltage at the bulbs - but obviously no higher than the battery voltage).
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Re: DIY: Relays for dim headlights

Post by Naviuk »

Hi

I did this change when i installed the "Angel" eyes on my old Polo.

One thing i would recommend is making sure that the relay switch itself is protected from water or anything else that could possible make it wet...

I had a nasty experience where i went outside one day and saw my car lights on. as you can imagine first instinct is it's being Stolen! but it turned out the relay had got wet and shorted, making the lights come on...

I went down to A1 radio and bought two cases just bigger then the relays, cut some holes for the wireing and then sealed the unit with silicon... this made a massive difference and never gave me a days problem :)

use it, don't use it... my 2 cents worth :)

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Re: DIY: Relays for dim headlights

Post by Viral_88 »

Naviuk wrote:Hi

I did this change when i installed the "Angel" eyes on my old Polo.

One thing i would recommend is making sure that the relay switch itself is protected from water or anything else that could possible make it wet...

I had a nasty experience where i went outside one day and saw my car lights on. as you can imagine first instinct is it's being Stolen! but it turned out the relay had got wet and shorted, making the lights come on...

I went down to A1 radio and bought two cases just bigger then the relays, cut some holes for the wireing and then sealed the unit with silicon... this made a massive difference and never gave me a days problem :)

use it, don't use it... my 2 cents worth :)

Cheers
My relays are mounted up next to the battery on my golf 3 and i haven't had any bad wet weather experiences . . .yet :smile: But don't get me wrong that is a good idea to seal them off like that
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Re: DIY: Relays for dim headlights

Post by iceblue »

Yes, sealing it is a good idea. I used the heatshrink on the push on terminals and then wrapped insulation tape around the connectors and relay, starting at the wire and wrapping the tape around and up until the relay was covered. (I started at the bottom and wrapped upwards so that the tape at the top overlapped the tape below it, meaning water cant run in between the layers of tape).

Of course some sort of enclosure like Naviuk used would be best.
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Re: DIY: Relays for dim headlights

Post by U3 »

i haveone question on this. why connect the current earth of the headlights to the earth of the new relay?

i did it a short while ago.. i set up with the Relay being earthed but i never connected the headlight earths to the new relay's earth.

The HOWTO i read didnt mention that.
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Re: DIY: Relays for dim headlights

Post by iceblue »

U3 wrote:i haveone question on this. why connect the current earth of the headlights to the earth of the new relay?

i did it a short while ago.. i set up with the Relay being earthed but i never connected the headlight earths to the new relay's earth.

The HOWTO i read didnt mention that.
Are you referring to this picture: ?

Image

If yes, all I did was ground the relay at the headlight ground instead of running a cable all the way back to the battery. Once you have run the new ground cable from the battery to the headlight connector, the headlight connector is now grounded and you can just connect the ground terminal of the relay to it, instead of all the way to the battery.
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