Car headlights, wiring modification relay problem.

Discussion in 'General Electronics Chat' started by JTP, Jan 21, 2009.

  1. JTP

    Thread Starter New Member

    Jan 21, 2009
    I put some aftermarket headlights in my car a while ago, and they use two different bulbs in each side, one for low beams and one for high beams. Normally, when you turn on the high beams, the low beams turn off. I found a wiring modification how-to that explains how to add a relay (simple 1P2T 12V 30A automotive relay) to the circuit so that the low beams stay on when the high beams are switched on. This really improves the light output of the car.

    I did this and it works great.

    My problem is that I live in Canada and my car has daytime running lights. DRLs run the high beams at half voltage whenever the low beams are off and the e-brake is off. When the DRLs are on, the relay gets confused by the half voltage and it buzzes like crazy, and all 4 lights flicker.

    Is there any way to somehow send signal to the relay only when it's recieving a full 12V or more? Or any other way around this problem? Or should I just take the whole thing out...

    Thanks for looking.
  2. mik3

    Senior Member

    Feb 4, 2008
    Take another relay 2 and connect its normally open contacts in series with relay 1. Then connect the coil of the relay 2 to the low beam wire and zero volts. When the low beams are off, relay 2 will be off and not allowing relay 1 to turn on. When you switch on the low beams relay 2 will turn on and allow relay 1 to turn on if the high beams are turned on.
    A problem which may occur is that the low beams switch off faster than the high beams turn on and relay 2 switches off before relay 1 conducts to power the lower beams. Try it and if you have this problem connect a 3300uF capacitor in parallel with the relay which controls the low beams (not the added one but the original one).
  3. mikeross

    New Member

    Oct 2, 2009
    Just replaced my headlights and I noticed that one shines brighter than the other. What could be the problem with it? Does it have to do with wiring or was it my installation? Thanks
    Last edited: Oct 9, 2009