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Headlight wiring

  • 18-11-2012 2:11pm
    #1
    Ronnie Beck
    Closed Accounts Posts: 1,452 ✭✭✭


    I'm looking to rewire my headlights using 4 relay's to increase the volts at the bulbs(h4's). I've two quick questions.

    I have 8 amp 2.7mm diameter auto wire here. Will that be sufficient or would a bigger gauge be better?

    I'm going to use two spare blade fuse slots in the fuse box above the battery with 20 amp fuses. Should be about 14v. Should I send the + feed from each of these fuses to 2 relays at each headlight or to each beam?


Comments

  • #2
    Chimaera
    Registered Users, Registered Users 2 Posts: 1,652 ✭✭✭Chimaera


    What car is this on? Unless it's really old, or American, your car should already have a relay system controlling the headlights, with separate relays and fuses for low and high beam on each side.

    FWIW, 8 A @ 14 V = 112 W - most headlamp bulbs are 55 or 60 W.


  • #3
    Ronnie Beck
    Closed Accounts Posts: 1,452 ✭✭✭Ronnie Beck


    Chimaera wrote: »
    What car is this on? Unless it's really old, or American, your car should already have a relay system controlling the headlights, with separate relays and fuses for low and high beam on each side.

    FWIW, 8 A @ 14 V = 112 W - most headlamp bulbs are 55 or 60 W.

    It's a '03 VW transporter with no relay's unfortunately. I'm only getting 10.5 volts at the bulbs. It's pretty bad driving in the dark this time of year. ...insert rant about ebay hid kits on civic's in the west of ireland... That 8 amp cable should do for most of it but I think I'll get 17 amp wire for the earths from the bulbs and some other sections. Thinking about it since, some parts of the loom will be feeding the two bulbs or the two filaments at once. Two high beams at 14v is around 8.5 amps.

    Does a normal car use 2 or 4 relays for a pair of H4 bulbs?


  • #4
    Eric Cartman
    Registered Users, Registered Users 2 Posts: 26,280 ✭✭✭✭Eric Cartman


    Ronnie Beck wrote: »
    It's a '03 VW transporter with no relay's unfortunately. I'm only getting 10.5 volts at the bulbs. It's pretty bad driving in the dark this time of year. ...insert rant about ebay hid kits on civic's in the west of ireland... That 8 amp cable should do for most of it but I think I'll get 17 amp wire for the earths from the bulbs and some other sections. Thinking about it since, some parts of the loom will be feeding the two bulbs or the two filaments at once. Two high beams at 14v is around 8.5 amps.

    Does a normal car use 2 or 4 relays for a pair of H4 bulbs?

    some cars use a relay per bulb others use 1 relay per set of bulbs, depends on how the manufacturer designed it.

    for H4's You could use 1 30 amp relay ( 1 runs of 12-14awg cable going to each headlight terminating at the relay and a length of 10awg cable going from the relay to the battery, or run 2 relays and connect the whole lot with 12-14awg


  • #5
    Ronnie Beck
    Closed Accounts Posts: 1,452 ✭✭✭Ronnie Beck


    I was thinking of using the four to spread out the load a bit so the relays last longer. Overkill? Definitely going to use at least two. Don't want to be relying on the one relay.


  • #6
    Chimaera
    Registered Users, Registered Users 2 Posts: 1,652 ✭✭✭Chimaera


    I can't find a reference to any relays being used for the headlights on this so yuo may be right.

    You do have 4 fuses for the headlights though, 2 for low-beam (left and right) and 2 for high-beam (also for left and right).

    You will need at least 2 relays: one each for low and high beam. If you do this, you need to make sure each relay can drive two output circuits.

    The relay will be switched from the relevant headlamp switch and will drive the headlamps through the existing fuses. You'll need a high current wire from the battery to the relay to drive the lamps.

    I've done a quick sketch of what I think your original setup should be and what you should be looking at doing on your new setup.

    http://imgur.com/yAxQj

    I'll have another look at this later on when I'm at home.


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  • #7
    Ronnie Beck
    Closed Accounts Posts: 1,452 ✭✭✭Ronnie Beck


    Thanks for your help. I not a natural electrician but I'll hopefully get there in the end. Here's my first sketch. I still haven't decided which wires go where yet and a few other bits.

    scandr.jpg

    I'm thinking off running it all from this small fusebox on the side of the battery. The second terminal from right is free on mine too. It's the 50 amp fuse in the diagram. Not sure on how to split the wires up between this terminal and the relay. A two relay system would probably make this easier.DSC00381.jpg


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