Why is there a relay on my headlight?

[Nj]

Question... what would someone put a relay on the back of one headlight and run a live connection from the battery to it? only on one side too. I assume the dangling wire was an earth that has come free.


Thoughts anyone?

[UrS4boy]

Question... what would someone put a relay on the back of one headlight and run a live connection from the battery to it? only on one side too. I assume the dangling wire was an earth that has come free.Thoughts anyone?

Because before the advent of cheap HID bulbs and ballasts, people popped 100W bulbs into their headlights. That amount of current flowing only through the head light switch on the column stalk would melt it. Hence the relay, triggered by the head light switch but the actual power coming from the battery. That set-up lacks the proper fuse to prevent an issue with wiring under the hood causing your car to burn to the ground.

Just sayin'.

With aftermarket HID systems now available putting out more lumens for less current draw than the stock bulbs, such relays, etc are no longer needed.

[AndyP]

More volts to the bulb if you relay a direct feed from the battery, makes the lights brighter.

[Nuvo]

Hi Noel, have a read here to find the answer to your question.

[K Simmonds]

I forgot to mention that I discovered why the lights are so good on the car, as Andy says they've been relayed in order to get more voltage. I didn't spot the bare wire, can you see where it's been dislodged from, maybe you caught a connection whilst fixing the PAS pipe?

[UrS4boy]

I forgot to mention that I discovered why the lights are so good on the car, as Andy says they've been relayed in order to get more voltage. ?

While that would be true, it is more likely that is was done so the filament bulbs could be upsized to ones with more wattage. What is in there now?

[mdz]

As above, relaying lights straight from the battery using decent wires (especially the ground) you will get more light with the same 55w bulbs. It's nothing new, I have this on my to-do list for a long time. OEM wires are way too thin for required current.
And this saves lights switch from melting.

[Nj]

thanks lads. That's all genuinely appreciated.

OK, that makes a bit of sense. Although it's only on one side, so I guess the 12v feeds straight into the loom at that side and increases the voltage to both sides right?

There's definitely no hint of an HID setup, which would blind the **** out of everyone with the reflector lenses. I'm not sure what bulbs I just pulled out of there but I put in a pair of Nightbreakers purely because I know they're good. The wiring's bloody awful. The loose wire I took to be a ground/earth because I couldn't find anything else that it could have possibly been connected to. The 12v feed from the battery is several pieces of wire connected together with no fuse so I should really replace that completely with a heavier wire, properly connected and fused. The pins on the relay weren't protected either so when I took out the headlight the relay swung over and I got a spark as one of the pins hit part of the slam panel. I have that all temporarily taped up to insulate it for now. In an ideal world that relay should be in the main relay/fuse box.

fack, I'm taking it for MOT tomorrow so I assume they aren't going to like that. I might have to find time to sort it out in the morning.

Kit, yeah that definitely explains why you thought the lights were so good I'll check and see what wattage those bulbs I pulled out are.

[Nj]

good price for night breakers by the way if anyone needs a pair
http://www.ebay.co.uk/itm/151810992015

[K Simmonds]

thanks lads. That's all genuinely appreciated.

OK, that makes a bit of sense. Although it's only on one side, so I guess the 12v feeds straight into the loom at that side and increases the voltage to both sides right?.

Yep, the relay will be feeding both headlight looms with current directly from the battery, their both equally as bright so should both be connected.

Yes, the feed should be fused and all live connections covered, sorry I didn't do it before the car left but I was more concerned about the about the other electrical gremlins to pay it much attention.

[Nj]

don't be daft mate. you had loads to do and if it hadn't been for you I doubt the car ever would have left the UK. It certainly wouldn't have been roadworthy when it landed in germany. so minor things like this dodgy wiring are totally fine for me to handle.
where would the fun be if I didn't have something to fix?

[K Simmonds]

Thank mate, I really should of had a better look though, un-fused lives straight from battery aren't very cool. But as the headlights were one of the the things that worked well I figured I should just leave it alone and concentrate on the important stuff.

I'd keep the set up that's there just tidy it up and redo the feed from the battery with decent thickness black insulated wire, add a fuse and make sure all live connections are covered.

[Bowie69]

Take it off the back of the alternator and gain a few more lumens... saves the volts drop between alternator and battery then, and a shorter run of wires too.

[John.]

Take it off the back of the alternator and gain a few more lumens... saves the volts drop between alternator and battery then, and a shorter run of wires too.

Nice one batman!

Haven't wired in a relay yet to my car.......but I was thinking if you use the headlight feed to switch the relay, and that supplies the same wire that you've tapped into(?), wouldn't there need to be another switch to interrupt the supply to pin 85/86.........or I'm thinking the relay will just stay in the closed position as it's supplying the switched feed from pin 87.
I KNOW there'll be a simple explanation, can someone shed light?

[Nj]

I know that was English John but for the life of me I have no idea what it means
But that's probably just because I haven't given this enough consideration. Henkjan just gave me this link in my project thread, which should be useful.

http://audi100.net/Technik/Tips___Tr...chtupdate.html

Taking the feed from the alternator sounds like a fine idea. I'll most likely do that and just make sure I have a safe solution to keep me going until the weather warms up enough that my hands don't keep cracking open like burst sausages.